The minimum supply of health services which should be generally and uniformly available in order to assure adequate health status and protection of the population from disease, or to meet some other criteria or standards. Given that all possible services cannot be supplied to the entire population, it is surprising how little definition or discussion there has been of what set of services constitutes an appropriate minimum and of how to assure its availability. A beginning has been made in Federal policy with the definition of required services for Medicaid and basic health services required of HMO’s for Federal assistance or qualification. These include: physician services, hospital services, medically necessary emergency care, preventive health services, home health services, up to 20 visits of outpatient mental health services, medical treatment and referral services for alcoholism and drug abuse, and laboratory and rediologic services (section 1802(1) of the PHS Act). Where a minimum is defined, a higher level of service is usually also defined (supplemental health and optional services for HMOs and Medicaid, respectively). It is not clear in either case whether the higher level is thought of as all other, all other needed, or all other affordable services.