Top Private Hospitals in the USA: Complete Healthcare Guide

The United States has a large and diverse hospital system that includes government-owned facilities, private nonprofit hospitals, academic medical centers, and investor-owned hospital networks. For patients seeking highly specialized treatment, many of the country’s most prominent medical centers are private nonprofit institutions affiliated with universities or large health systems.

Choosing among them requires more than looking at reputation. A hospital that is well suited for complex cancer surgery may not be the most appropriate choice for cardiac rehabilitation, transplantation, pediatric care, or a routine procedure close to home. Insurance network status can also make a major difference in what a patient ultimately pays.

This guide examines prominent private hospitals and academic medical centers across the United States, their major areas of clinical focus, and the practical issues patients should evaluate before arranging treatment. It also explains hospital pricing, health insurance, self-pay estimates, international-patient considerations, and how to compare hospitals using reliable information rather than promotional claims.

Freshness note: Hospital services, physician rosters, insurance networks, and prices can change frequently. Readers should confirm current details directly with the hospital and insurer before making a healthcare or financial decision.

What Does “Private Hospital” Mean in the United States?

A private hospital in the United States is generally a hospital that is not owned by a federal, state, county, or municipal government. Private hospitals can operate under different ownership structures.

  • Private nonprofit hospitals: These institutions reinvest revenue into patient care, facilities, research, education, and community programs rather than distributing profits to private shareholders.
  • Private for-profit hospitals: These hospitals may be owned by companies or investors and operate as commercial businesses.
  • Private academic medical centers: Many university-affiliated hospitals are nonprofit organizations combining patient care with medical education, clinical research, and specialty programs.

Some of the best-known U.S. medical centers are private nonprofit hospitals rather than traditional commercial private hospitals. That distinction matters because “private” does not automatically mean luxury care, faster access, or higher quality. It mainly describes ownership.

Private Hospitals vs. Public Hospitals

Feature Private Hospital Public Hospital
Ownership Nonprofit organization, university system, company, or other private entity Federal, state, county, city, or other government entity
Patient population May serve insured, Medicare, Medicaid, self-pay, and international patients Often has an important safety-net and community-care role
Specialized services Many operate major specialty centers and research programs Varies widely; some public hospitals are major trauma and academic centers
Insurance Network participation depends on the hospital and insurance plan Network participation also varies by hospital and plan
Price Not necessarily more or less expensive solely because of private ownership Actual patient cost depends on coverage, service, network status, and other factors

Ownership alone should not be used as a quality measure. Patients should instead examine clinical expertise, physician qualifications, procedure volume where reliable data are available, safety information, insurance participation, location, and the services needed for their specific condition.

Leading Private Hospitals and Academic Medical Centers in the USA

The institutions below are not presented as a numerical ranking. They are prominent private nonprofit hospitals or academic medical centers known for providing advanced specialty care. Clinical programs and availability can change, so patients should review the institution’s current website and consult their medical team before deciding where to seek treatment.

Mayo Clinic Hospital and Mayo Clinic Rochester

Location: Rochester, Minnesota, with major Mayo Clinic campuses in Arizona and Florida
Official website: Mayo Clinic

Mayo Clinic is a private nonprofit medical organization that combines specialist care, research, and education. Its multidisciplinary model is particularly relevant for people with complicated diagnoses that may require evaluation by doctors from several specialties.

Major Areas of Care

Mayo Clinic provides services across fields including cardiology, cardiovascular surgery, cancer care, neurology, neurosurgery, transplantation, gastroenterology, orthopedics, endocrinology, and complex internal medicine.

Patients who have an unusual condition, need a second opinion, or require coordination among multiple specialists may consider investigating Mayo Clinic. However, referral requirements, appointment availability, and insurance coverage should be checked before travel is arranged.

Cost and Insurance Considerations

A patient should verify whether both the Mayo facility and the individual clinicians involved are covered by the patient’s plan. Complex care can generate separate charges for physician services, imaging, laboratory testing, procedures, anesthesia, pathology, and hospital facilities.

Cleveland Clinic

Location: Cleveland, Ohio, with additional locations in the United States and internationally
Official website: Cleveland Clinic

Cleveland Clinic is a nonprofit academic health system with extensive specialty and subspecialty services. It is widely associated with cardiovascular medicine but also provides care in many other complex medical fields.

Major Areas of Care

Programs include heart and vascular medicine, neurology and neurosurgery, digestive disease, cancer care, orthopedics, urology, transplantation, respiratory medicine, and other medical and surgical specialties.

Patients considering highly specialized surgery should ask whether the recommended procedure is performed at the main Cleveland campus or at another facility within the system, because services and insurance participation may differ by location.

The Johns Hopkins Hospital

Location: Baltimore, Maryland
Official website: The Johns Hopkins Hospital

The Johns Hopkins Hospital is part of Johns Hopkins Medicine and is closely integrated with medical education and research. It provides tertiary and quaternary care for patients who require advanced diagnostic or surgical services.

Major Areas of Care

Its clinical programs include cancer, neurology and neurosurgery, cardiology, transplantation, ophthalmology, pediatrics, psychiatry, rheumatology, and a broad range of surgical specialties.

Patients traveling to Johns Hopkins for complex care should determine which hospital, outpatient center, or specialist will provide each component of treatment. Coverage can vary even within a large academic system.

Massachusetts General Hospital

Location: Boston, Massachusetts
Official website: Massachusetts General Hospital

Massachusetts General Hospital is a nonprofit academic medical center affiliated with Harvard Medical School and part of Mass General Brigham. The hospital provides both general hospital services and complex subspecialty care.

Major Areas of Care

Clinical programs cover cancer, heart and vascular disease, neurology, neurosurgery, orthopedics, transplantation, digestive disorders, psychiatry, and numerous medical and surgical specialties.

For patients comparing Boston-area hospitals, physician expertise and insurance network participation may be more useful than relying on institutional reputation alone. Some insurance plans have tiered hospital networks that can change cost-sharing even when a facility is technically covered.

NewYork-Presbyterian Hospital

Location: New York City, New York
Official website: NewYork-Presbyterian

NewYork-Presbyterian is a nonprofit academic health system associated with Columbia University Vagelos College of Physicians and Surgeons and Weill Cornell Medicine. It operates multiple campuses in New York City and the surrounding region.

Major Areas of Care

Its services include cardiovascular care, oncology, neurology and neurosurgery, transplantation, pediatrics, women’s health, orthopedics, and emergency and critical care.

Patients should identify the specific campus at which treatment will occur. A health system may have multiple hospitals, outpatient sites, physician groups, and laboratories, and network participation can differ among them.

Cedars-Sinai Medical Center

Location: Los Angeles, California
Official website: Cedars-Sinai

Cedars-Sinai is a nonprofit academic medical center serving Southern California and patients referred for specialty treatment. It operates research, education, hospital, and outpatient programs.

Major Areas of Care

Services include cardiology and cardiac surgery, cancer treatment, digestive diseases, neurology and neurosurgery, orthopedics, transplantation, women’s health, and other specialty fields.

Patients traveling to Los Angeles should factor transportation, lodging, follow-up appointments, and the location of outpatient services into their planning. Treatment often involves more than the hospital admission itself.

Stanford Health Care

Location: Stanford and Palo Alto, California
Official website: Stanford Health Care

Stanford Health Care is an academic health system associated with Stanford University School of Medicine. It provides routine and highly specialized services and participates in clinical research and medical education.

Major Areas of Care

Major programs include cancer treatment, cardiovascular medicine, neuroscience, transplantation, orthopedics, digestive health, and advanced surgical care.

Patients interested in clinical trials should distinguish between standard treatment and research participation. Eligibility for a clinical trial is based on specific medical criteria and does not guarantee access to an experimental treatment.

Northwestern Memorial Hospital

Location: Chicago, Illinois
Official website: Northwestern Memorial Hospital

Northwestern Memorial Hospital is the flagship academic hospital of Northwestern Medicine and is affiliated with Northwestern University Feinberg School of Medicine.

Major Areas of Care

Services span cardiovascular care, oncology, neuroscience, orthopedics, transplantation, women’s health, digestive diseases, and numerous surgical specialties.

People considering treatment in Chicago should ask whether testing, surgery, rehabilitation, and follow-up can all be completed within the same network, particularly if their insurer has restrictions on outpatient facilities or rehabilitation providers.

Duke University Hospital

Location: Durham, North Carolina
Official website: Duke University Hospital

Duke University Hospital is an academic medical center within Duke University Health System. It provides complex referral care while supporting research and medical education.

Major Areas of Care

Programs include cancer, cardiovascular medicine, neuroscience, transplantation, orthopedics, pulmonary medicine, and a broad range of medical and surgical specialties.

Patients with serious chronic disease may want to ask how much follow-up must occur at Duke and how much can be coordinated with a physician closer to home. This can substantially affect travel and ongoing costs.

Houston Methodist Hospital

Location: Houston, Texas
Official website: Houston Methodist Hospital

Houston Methodist is a nonprofit health system, and its flagship hospital is located in the Texas Medical Center. The institution provides specialty and subspecialty care to patients from Texas, elsewhere in the United States, and abroad.

Major Areas of Care

Clinical programs include heart and vascular medicine, neurology and neurosurgery, cancer care, transplantation, orthopedics, digestive diseases, and advanced surgery.

Houston contains several major hospital systems within the same medical district. Patients should therefore verify precisely which facility, specialist group, imaging center, and laboratory will be involved in their care rather than assuming all Texas Medical Center providers share the same insurance arrangements.

Quick Comparison of Prominent Private Medical Centers

Hospital Location Examples of Major Specialty Areas
Mayo Clinic Rochester, Minnesota Cardiology, cancer, neurology, transplantation, complex diagnosis
Cleveland Clinic Cleveland, Ohio Heart and vascular, neurology, digestive disease, orthopedics
The Johns Hopkins Hospital Baltimore, Maryland Neurology, cancer, transplantation, ophthalmology, surgery
Massachusetts General Hospital Boston, Massachusetts Cancer, cardiovascular care, neuroscience, transplantation
NewYork-Presbyterian New York, New York Cardiology, neurology, transplantation, pediatrics, oncology
Cedars-Sinai Los Angeles, California Heart care, cancer, transplantation, digestive disease
Stanford Health Care Stanford, California Cancer, cardiovascular medicine, neuroscience, transplantation
Northwestern Memorial Hospital Chicago, Illinois Cardiology, oncology, neuroscience, transplantation
Duke University Hospital Durham, North Carolina Cancer, heart care, neuroscience, transplantation
Houston Methodist Hospital Houston, Texas Cardiovascular care, neuroscience, cancer, transplantation

This comparison is intended to help readers begin their research. It should not be interpreted as a ranking or a recommendation for a specific diagnosis.

How to Compare Hospitals Beyond Reputation

Brand recognition can be useful when creating an initial shortlist, but it does not answer the most important question: which hospital and medical team are appropriate for a particular patient and condition?

Look at the Relevant Specialty, Not Just the Hospital

A large hospital may have excellent programs in several fields, but the specific department, surgeon, oncologist, neurologist, or multidisciplinary team is what matters for individual care.

Questions worth asking include:

  • Does the hospital regularly treat the patient’s specific diagnosis?
  • Which specialist would be responsible for care?
  • Is a multidisciplinary review available when appropriate?
  • What diagnostic tests are required before an appointment?
  • Where will surgery, imaging, rehabilitation, and follow-up take place?
  • Can part of the follow-up care be coordinated with the patient’s local physician?

Use Government Comparison Tools Where Appropriate

The Centers for Medicare & Medicaid Services provides Medicare Care Compare, which allows consumers to review information about hospitals and other healthcare providers. Public reporting does not capture every factor relevant to an individual case, but it can provide additional context beyond marketing material.

Review Physician Credentials

Patients can review a physician’s specialty training, board certification where applicable, state licensure, hospital affiliations, and experience with the relevant condition or procedure. A hospital’s prestige should not substitute for evaluating the actual clinician who will provide treatment.

Hospital Treatment Costs in the United States

There is no single reliable price for “treatment at a private hospital.” The final cost depends on the diagnosis, procedure, length of stay, hospital, physician fees, insurance contract, deductible, coinsurance, medications, imaging, laboratory work, anesthesia, pathology, and complications or additional services that become necessary.

A hospital may publish a standard charge, discounted cash price, or insurer-negotiated rate. None of these figures automatically equals what a specific insured patient will owe.

Why the Same Procedure Can Have Different Prices

Treatment or Service Cost Considerations Main Factors Affecting Price
Emergency visit Charges vary according to evaluation and services required Emergency severity, testing, imaging, physician services, admission
Outpatient surgery Facility and physician charges may be separate Procedure complexity, anesthesia, surgeon, pathology, implant use
Inpatient surgery Total cost may include multiple professional and facility bills Length of stay, operating room, specialists, drugs, complications
Cancer treatment Costs differ substantially by diagnosis and treatment plan Surgery, radiation, medications, infusions, imaging, laboratory testing
Diagnostic imaging Price varies by study and facility MRI, CT, contrast material, interpretation, site of service
Rehabilitation May be billed separately from the hospital episode Setting, number of sessions, therapist, insurance benefits

Hospital Price Transparency

Federal hospital price-transparency requirements generally require U.S. hospitals to make certain pricing information publicly available, including machine-readable files and consumer-friendly information for shoppable services. The Centers for Medicare & Medicaid Services hospital price transparency resource explains the federal requirements.

Price-transparency files can be difficult for consumers to interpret. A listed amount may represent a standard charge, cash price, or negotiated rate rather than a patient’s final responsibility.

Request an Individualized Estimate

Before scheduled care, ask the hospital for an estimate based on the exact procedure, location, and insurance information. Then ask the insurer to calculate expected patient responsibility using current benefits and network status.

Patients without insurance should specifically ask whether the hospital has a self-pay rate, financial-assistance policy, payment plan, or other assistance program for which they may qualify.

Understanding Health Insurance at Private Hospitals

Having insurance does not automatically mean every service at a private hospital will be inexpensive. The amount a patient pays depends on the plan’s benefits and how the hospital, physicians, and other providers participate in the plan’s network.

Insurance Term What It Generally Means
In-network A provider or facility has contracted with the health plan under network terms
Out-of-network A provider does not participate in the plan’s applicable network; coverage may be reduced or unavailable depending on the plan and circumstances
Deductible The amount a patient generally pays for covered services before certain plan benefits begin paying
Copayment A fixed amount that may be charged for a covered service
Coinsurance A percentage of an allowed cost that a patient may owe after applicable plan rules are met
Out-of-pocket maximum A plan-defined limit on certain covered in-network cost sharing during a plan year; exclusions and rules apply
Prior authorization Approval that may be required from the health plan before certain services or treatments are provided

Consumers can review general insurance terminology through HealthCare.gov’s health insurance glossary.

PPO and HMO Plans

A Preferred Provider Organization, or PPO, often gives members more flexibility to obtain care from different providers, although out-of-network care can involve significantly higher patient costs. An HMO generally relies more heavily on a defined provider network and may require referrals or other plan-specific procedures for specialist treatment.

These are broad descriptions. The actual insurance contract controls coverage, not the plan label alone.

Medicare

Medicare beneficiaries should confirm that the hospital and clinicians participate appropriately with Medicare and determine how their specific Medicare coverage applies. Medicare Advantage plans may use provider networks and prior-authorization requirements that differ from Original Medicare.

Official coverage information is available at Medicare.gov.

Medicaid

Medicaid programs are administered jointly by federal and state governments, and eligibility, managed-care networks, and provider participation vary by state. A hospital that participates in one Medicaid arrangement may not necessarily participate in every managed-care plan available in that state.

Marketplace Insurance

People insured through Affordable Care Act Marketplace plans should verify the specific hospital and physician network for their exact plan. Information about Marketplace coverage is available through HealthCare.gov.

Five Insurance Checks to Complete Before Scheduled Treatment

  1. Confirm the hospital is in-network. Use both the insurer’s current directory and the insurer’s member services department.
  2. Confirm the physician is in-network. A hospital’s network status does not guarantee every physician practicing there has the same status.
  3. Check ancillary providers. Ask about anesthesiology, pathology, radiology, laboratories, rehabilitation, and other services that might generate separate bills.
  4. Verify prior authorization. Determine whether the procedure, admission, medication, imaging study, or other service requires insurer approval.
  5. Request an estimated out-of-pocket amount. Compare the hospital estimate with information from the insurer before proceeding with non-emergency treatment.

Why Hospital and Physician Bills May Be Separate

One of the most confusing aspects of U.S. healthcare is that a single episode of treatment can produce bills from multiple organizations.

A surgery, for example, can involve:

  • The hospital or outpatient facility
  • The surgeon
  • An anesthesiology group
  • A radiologist
  • A pathologist
  • A laboratory
  • Medical-device or implant-related charges
  • Post-acute rehabilitation services

Before elective treatment, ask the hospital which groups are likely to bill independently and whether those groups participate in the patient’s insurance network.

The No Surprises Act and Unexpected Medical Bills

Federal protections under the No Surprises Act address certain unexpected out-of-network bills in situations covered by the law, including many emergency services and certain services provided by out-of-network clinicians at in-network facilities. The rules contain important details and exceptions.

Patients can review official information at the CMS No Surprises resource. These protections do not mean every out-of-network service is automatically covered at an in-network rate, so consumers should still verify benefits before planned care whenever possible.

Private Hospitals for International Patients

Many large academic medical centers have departments that assist patients traveling from outside the United States. Available services may include appointment coordination, medical-record review, interpreter arrangements, estimated charges, and help organizing care across multiple departments.

The availability and scope of international-patient services differ by institution.

Documents Commonly Requested

An international patient may be asked to provide:

  • Passport or other identification
  • Medical records and physician summaries
  • Imaging files and radiology reports
  • Pathology reports or pathology material when relevant
  • Current medication list
  • Previous treatment records
  • Insurance or sponsorship documentation if applicable
  • Financial information or deposits required by the institution

Records may need to be translated into English, depending on hospital requirements.

Ask for a Treatment Plan and Financial Estimate

International patients should request an estimate before traveling, but the estimate should not be interpreted as a guaranteed final price. Additional diagnostic findings, complications, a longer admission, added procedures, or changes in the treatment plan can increase the total cost.

Patients should also budget for flights, accommodation, local transportation, meals, caregiver expenses, and possible extended stays for follow-up care.

How Self-Pay Patients Can Prepare

People who do not have insurance should not assume that a hospital’s highest published charge is necessarily the amount they will be asked to pay. Hospitals may publish discounted cash prices or have separate self-pay policies.

Before non-emergency care, ask the billing or financial counseling department:

  • What is the self-pay or cash price for the planned service?
  • Which professional fees are excluded from the estimate?
  • Is a deposit required?
  • Is financial assistance available?
  • What documentation is required to apply for assistance?
  • Are payment plans available?
  • How long is the estimate valid?

Nonprofit hospitals generally maintain financial-assistance policies, but eligibility and application rules differ. A patient should obtain the hospital’s current written policy rather than relying on verbal assumptions.

Questions to Ask Before Choosing a Private Hospital

Topic Question to Ask
Clinical expertise How frequently does the medical team treat my condition or perform the proposed procedure?
Specialist Which physician will be responsible for my treatment?
Insurance Are the hospital, physician, and likely supporting providers in-network for my exact plan?
Authorization Does my insurer require prior authorization or a referral?
Cost Can I obtain a written estimate of expected charges and patient responsibility?
Separate billing Which clinicians or services may bill me separately?
Follow-up Can follow-up care be provided closer to home?
Records Which medical records and imaging studies should I send before the appointment?

When Traveling to a Famous Hospital May Not Be Necessary

A nationally recognized academic medical center can be valuable for rare diseases, complicated diagnoses, highly specialized procedures, transplantation, advanced cancer care, unusual surgical cases, or a difficult second opinion. But many common conditions can be managed effectively at high-quality regional hospitals closer to home.

Travel can add lodging costs, time away from work, transportation expenses, and logistical problems during rehabilitation. Continuity with local physicians may also be easier when treatment occurs within the patient’s community.

A useful question for a treating physician is whether the patient’s condition genuinely requires a tertiary or quaternary referral center or whether comparable care is available locally.

Frequently Asked Questions

What are the top private hospitals in the USA?

There is no single objective list that identifies the best private hospital for every patient or condition. Prominent private nonprofit academic medical centers include Mayo Clinic, Cleveland Clinic, The Johns Hopkins Hospital, Massachusetts General Hospital, NewYork-Presbyterian, Cedars-Sinai, Stanford Health Care, Northwestern Memorial Hospital, Duke University Hospital, and Houston Methodist Hospital. The most appropriate hospital depends on the diagnosis, relevant specialty, physician expertise, insurance network, location, and financial considerations.

Are private hospitals better than public hospitals in the United States?

Not necessarily. Private or public ownership is not itself a measure of clinical quality. Some public hospitals are major academic, trauma, safety-net, and specialty centers, while many private nonprofit hospitals are internationally recognized academic institutions. Patients should compare the specific department, physician expertise, services, quality information, insurance participation, and suitability for the condition rather than choosing based solely on ownership.

How much does treatment at a private U.S. hospital cost?

There is no meaningful single nationwide price because costs differ by diagnosis, procedure, hospital, insurance plan, network status, physicians, medications, imaging, laboratory work, anesthesia, length of stay, and other services. Published hospital prices also do not necessarily equal an insured patient’s responsibility. For planned care, request an individualized estimate from the hospital and confirm expected cost sharing directly with the insurer.

Does health insurance cover private hospitals?

Many insurance plans cover treatment at private hospitals, but coverage depends on the specific plan and provider network. A hospital may participate with one product offered by an insurer while being out-of-network for another. Patients should verify the hospital, treating physician, facility, and supporting providers for their exact plan and determine whether prior authorization is required.

Can international patients receive treatment at private hospitals in the USA?

Yes. Many large U.S. academic medical centers have programs for international patients. Services can include medical-record review, scheduling, interpretation, and financial coordination. Requirements differ by hospital, and self-paying patients may need to provide financial information or make an advance payment. Patients should obtain the institution’s current international-patient requirements before arranging travel.

How can I check whether a hospital is in-network?

Start with your insurer’s current online provider directory, but do not rely on the directory alone for expensive scheduled care. Call the insurer using the member-services number on your insurance card and provide the hospital’s exact name and location. Also confirm the individual physician and any likely anesthesiology, radiology, pathology, or other groups. Keep a record of the date, representative, and reference number for the conversation when available.

Can I request a hospital cost estimate before treatment?

Yes. Patients should request an estimate before scheduled hospital care whenever practical. Ask whether the estimate includes the facility, physician, anesthesia, laboratory, pathology, imaging, medical devices, and other expected charges. Estimates are not always guarantees because medical needs can change during treatment. Insured patients should compare the hospital’s estimate with benefit information from their health plan.

What is the difference between a nonprofit and for-profit private hospital?

A nonprofit hospital generally reinvests surplus revenue in healthcare operations, facilities, research, education, or community programs rather than distributing profits to shareholders. A for-profit hospital can distribute profits to owners or investors. Both types are private rather than government-owned. Tax status alone does not determine whether a hospital is clinically appropriate for a particular patient.

Do Medicare patients use private hospitals?

Yes. Many private hospitals participate in Medicare. However, Medicare beneficiaries should confirm how the specific hospital and physicians participate and how their coverage applies. People enrolled in Medicare Advantage should pay particular attention to the plan’s provider network and prior-authorization requirements, which may differ from Original Medicare.

Why might I receive several bills after one hospital procedure?

Hospital care often involves multiple organizations or medical groups. A patient may receive separate bills from the hospital, surgeon, anesthesiologist, radiologist, pathologist, laboratory, rehabilitation provider, or other clinicians. Before elective treatment, ask which entities are expected to bill separately and verify their insurance status where possible.

Choosing the Right Private Hospital for Your Needs

The best hospital decision is usually based on a combination of clinical fit and practical realities rather than reputation alone. Start by identifying the specialty and level of expertise required for the diagnosis. Then compare physicians, available services, location, follow-up arrangements, insurance network participation, and expected patient costs.

For complex conditions, an academic medical center with multidisciplinary expertise may offer access to specialists, advanced diagnostics, research programs, and highly specialized procedures. For more routine treatment, a strong regional hospital closer to home may offer high-quality care with less travel and simpler follow-up.

Before committing to planned treatment, confirm the hospital and physician network, check prior-authorization requirements, request a written cost estimate, and determine which services may produce separate bills. International and self-pay patients should also discuss deposits, financial-assistance policies, and expected follow-up costs.

No hospital is the right choice for every patient. A qualified physician who understands the patient’s medical history can help determine whether referral to a particular specialty center is clinically appropriate.

Medical and Informational Disclaimer

This article is for general informational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. Hospital programs, physicians, prices, insurance networks, and coverage rules can change. Confirm current clinical and financial information directly with the hospital, healthcare professional, and insurance provider before making treatment decisions.

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