Prepaid health care plans are likely to play an important part in the current transition from inpatient to ambulatory care training of physicians, because such plans enroll one in seven Americans. In the spring of 1990, the Group Health Association of America conducted a survey of health maintenance organizations (HMOs) to assess their level of involvement in graduate medical education (GME). A questionnaire was sent to the 481 HMOs in the United States that had been operational for at least four years; 58% responded. Fifteen percent (42 HMOs) indicated that they were directly involved in GME. The majority of these 42 indicated that they had an agreement with an academic medical center (AMC) or a teaching hospital to serve as an ambulatory care rotation site. About one-sixth of the 42 HMOs had been approved by the Accreditation Council for Graduate Medical Education to serve as a sponsoring organization. HMOs directly involved in GME were more likely to be staff model and group model HMOs; older plans with an enrollment of 50,000 or more; not-for-profit plans; and those owned or sponsored by an AMC.