This study examines characteristics of volunteers participating in Phase I HIV vaccine trials. An understanding of these characteristics may assist in the recruitment of volunteers for future trials. Volunteer surveys from 232 participants were reviewed. A total of 95% of the volunteers were Caucasian, 69% were heterosexual, and 52% were women. Volunteers ranged in age from 19 to 60 years with a median age of 36. Among the volunteers, 73% knew someone who may have had AIDS or knew someone who was at risk for acquiring HIV. Volunteers cited personal and political reasons for participating in the vaccine trials. No "typical" volunteer was identified, supporting the belief that many factors affect a person's willingness to participate in such situations.