Recruitment of patients to clinical trials is a multi-stage process. To participate in a protocol, a patient must meet all the eligibility requirements; the physicians managing the patient must be amenable to enrolling the patient on protocol; and finally, the patient must consent to participate. In 1979, 64 clinical trials were open to patient accrual in the Division of Radiation Oncology, Mallinckrodt Institute of Radiology, St. Louis, Missouri. A total of 1103 cases were reviewed. Two hundred sixty-three patients were eligible for one of the protocols, of whom 124 were successfully recruited. The reasons for ineligibility and nonparticipation are discussed.