PARTICIPATORS AND NONPARTICIPATORS sarcoma clinical trials were given a standardized interview to identify causes for failure to randomize or for withdrawal from protocol treatments. Responses from the two groups were compared and analyzed. No differences were found the socioeconomic status of eligible patients w ho were participators or nonparticipators. Nine of .35 patients with tissue sarcoma would not accept randomization to caputution versus limb-sparing surgery plus irradiation; However, none of 39 patients with osteogenic sarcoma would not accept randomization to receive or not receive immunotherapy with BCG. It seemed that the signifieanee to the patient of treatment options determined by randomization influenced the patient's willingness to be randomized. Nearly all patients who withdrew from protocol treatments continued to receive medical care, but the standardized interview revealed that these treatments were less disrupting of daily activities than the protocol treatments received by participators. When the regrets expressed for personal suffering experienced as result of cancer treatments were tabulated, patients who withdrew more often expressed regret for receiving specific chemotherapeuttc treatments than did patients completing protocol treatments. These data suggest that patient nonparticipation (both unwillingness to be randomized and withdrawal from treatment protocols) was dependent on treatment-related factors. Surveys similar to this one in the context of a controlled clinical trial may help identify factors which cause patient nonparticipation and thereby help optimize trial management.