In the United States, racial differences in the prevalence and incidence of HIV infection and AIDS diagnoses are dramatic. These differences are large, have been recognized for nearly 20 years, and are as yet not well investigated. These disparities show no signs of diminishing and, in fact, are widening, particularly among drug users and women. Most observers of the racial disparities in prevalence and incidence of HIV infections and AIDS diagnoses in the United States have concluded that these disparities exist because prevention messages, supplies, and/or interventions do not effectively reach those at greatest risk of infection. In essence, such interpretations suggest that Blacks and Latinos continue to practice more risk behaviors than Whites. There are much data to suggest that this is, in fact, not true. Evidence from 232 'index' injection drug users and 465 of their drug and sexual network members participating in HIV Prevention Trials Network 037 is presented. These data describe lower use and/or access to drug treatment and needle exchange programs by Black injectors. In addition, data indicate the coexistence of increased prevalence of HIV in the networks of uninfected Black drug users and fewer associated risk behaviors in the networks of Black and Latino indices compared with networks of White indices. Understanding racial disparities in HIV is a critical challenge; yet, risk behaviors alone do not explain observed disparities in infection rates.