Of these, 13 were seropositive, 5 were bisexual/homosexual males, and 3 were female prostitutes. Of participants, 95 percent reported sharing needles. Compared to seronegatives, seropostives were likely to have higher annual salaries, inject drugs in shooting galleries, and speedball (combine cocaine and heroin) or boot (withdraw blood into the syringe before injecting). Further, seropositives were more likely than seronegatives to have been previously incarcerated. The HIV seroprevalance rate of 1.8 percent among intravenous drug users was surprisingly low for this large metropolitan area. The epidemiological characteristics are consistent with the low seropositivity rates found in this study. Possible explanations for this low rate, compared with rates found on the East Coast, may be related to differences in patterns of drug use and the sexual and ethnic makeup of the sample. Risk reduction efforts among this population must be expanded before the HIV prevalence rate increases. 1 table, 1 note, and 6 references. (Author abstract modified)