A form of organization for physician services, in a health care plan, in which the plan (the third party payer) establishes a roster of physicians who are believed to be cost-effective. All services covered by the plan, when furnished by these physicians, are without charge to the beneficiary. The beneficiary may elect care from physicians not on the roster, but if she does, at least part of those providers’ fees must be paid by the beneficiary (or, in some forms of health insurance programs, by the physicians making up the roster of preferred providers).