HIV antibody was detected through the ELISA and Western blot tests in the serum of 178 (39.4 percent) of the 452 participants. Of these, 49.1 percent were black, 41.8 were Hispanic, and 17.2 percent were non-Hispanic white. The presence of HIV antibody was associated with the number of injections per month, particularly injections with used needles and with cocaine, and with injections with shared needles. The number of heterosexual sex partners who used IV-drugs was an important risk factor for HIV infection in women and the only factor for IVDUs who had not injected after 1982. In addition, the detection of HIV antibody was independently associated with being black or Hispanic, more recent year of the last injection of drugs, drug injection in shooting galleries, IVDU sex partners, and low income. The findings of this study indicate that for IVDUs the risk of acquiring HIV infection is dependent on the interaction of several variables including drug use and sexual behavior, increasing seroprevalence, and race or ethnic background. 5 tables and 26 references (Author abstract modified)