Thirty-two men who participated in a trial of Zidovudine (> 500 CD4 cells/106 L) were surveyed regarding their reasons for participation in clinical trials. The major source of influence to enter the trial was the clinic doctor, and importance for self in participation was rated as the least important reason. Medical science and medical researchers were seen as the major beneficiaries. Being seen to do something about one’s illness was also seen as being important and probability of delaying AIDS was rated lowest. Chance of occurrence of risks of treatment were rated as slightly below 50%. Results of Flesch and Fry tests of informed consent documents suggested that they were written in the style of a scientific article, required the readability level of a university graduate and that recall was imperfect. Those who saw more benefits in their trial participation appeared to be most knowledgeable. These data suggest that participation in this clinical trial was based on altruistic, rather than personal reasons and that participants had realistic perceptions of outcomes.