Drugs must be tested in human clinical trials before they can be approved for marketing in the United States. These trials are often conducted by contract research organizations (CROs) that offer financial incentives to those who participate. The objectives of this study were to identify the motivations and barriers to participation in clinical drug studies. A survey was distributed to individuals at a CRO, who were either completing participation or were being screened for participation in a clinical drug study, and to a sample of university students. Responses were obtained from 195 people who participated and 68 people who considered participating in a clinical drug study. The motivations for participating were financial compensation, improvement of health, and contribution to science. Those who considered participating opted not to because of schedule conflicts, the risk involved, or potential discomfort from the medical procedures or medication.