Although most primary care physicians participate in state Medicaid programs, they may accept all Medicaid patients, or they may choose to limit their participation. This decision allows physicians to adjust their Medicaid caseloads to a desired level, and it has important implications for the access of low-income patients to health care. Surveys of pediatricians in 1978 and 1983 indicate that the proportion of pediatricians limiting their Medicaid participation increased significantly from 26 percent to 35 percent (p > .001). In addition, in both 1978 and 1983, limited participants saw significantly fewer Medicaid patients than full participants. This paper describes a number of strategies available to federal and state policymakers for fostering full Medicaid participation. Multivariate analyses indicate that increasing reimbursement levels is an important strategy for encouraging full Medicaid participation. In addition, full participants will increase their Medicaid caseloads in response to a variety of Medicaid policy incentives, while limited participants are found to respond to fewer policy incentives. The authors conclude that caution will be needed to ensure that health care cost-containment strategies such as capitation or selective contracting do not inadvertently discourage participation among both full and limited Medicaid participants.