The relative absence of racial/ethnic minorities among medical research subjects is receiving considerable attention because of recent government mandates for their inclusion in all human subject research. We examined racial differences in the prevalence of sociocultural barriers as a possible explanation for the underrepresentation of African Americans in medical research studies. During 1998-1999, a total of 198 residents of the Detroit Primary Metropolitan Statistical Area (PMSA) participated in a survey that examined impediments to participation in medical research studies. Chi square tests and logistic regression analyses were used to examine the association between race, issues related to trust of medical researchers, and the willingness to participate in medical research studies. Study results indicate that African Americans and whites differ in their willingness to participate in medical research. Racial differences in the willingness to participate in a medical research are primarily due to the lower level of trust of medical research among African Americans. African American respondents were also somewhat less willing to participate if they attribute high importance to the race of the doctor when seeking routine medical care, believed that minorities bear most of the risks of medical research, and if their knowledge of the Tuskegee Study resulted in less trust in medical researchers. These data reiterate the need for medical researchers to build trusting relationships with minority communities. Researchers can begin by acknowledging the previous medical abuse of minority research participants, discussing their specific plans to assure the protection of study participants, and explaining the need for the participation of racial/ethnic minorities including studies that specifically target or that are likely to result in disproportionate representation of racial/ethnic minorities among study participants.