In order to understand better why patients do or do not participate in clinical drug trials, we sent questionnaires to 100 patients with rheumatoid arthritis (RA) who participated in clinical drug trials at our center and to 100 RA patients with similar disease durations who did not participate in clinical drug trials at our center. We compared demographic, socioeconomic, and clinical characteristics of respondents. Those who participated and those who did not participate in clinical drug trials selected similar rank-order preferences of potential reasons for doing so. The most frequent reasons cited by participants and nonparticipants were physician recommendation (50% and 56%) and benefit to society (25% and 17%). Participants and nonparticipants were similar in reference to their age, sex, educational level, reported income per household, employment status, distance from the medical center, disease duration, number of tender joints, American Rheumatism Association functional class, and mean erythrocyte sedimentation rate variables. There were two differences between the groups: participants included a lower percentage of blacks and had a greater number of swollen joints. Even with those exceptions, we concluded that participants in clinical trials appear to be comparable to the general population of RA patients followed at our outpatient department.