The overall HIV infection rate was 61 percent. The study showed that IVDUs practicing high risk behaviors such as polydrug use, IV heroin and cocaine use, sex with multiple partners, and sex without using condoms were significantly more likely to be HIV positive than those who did not. The route of drug administration was significantly related to HIV seroprevalence status; those who took heroin and cocaine IV were significantly more likely to be HIV-positive than those who used it intranasally. Polydrug users were more prone to be HIV positive as compared with heroin users. No significant differences were found between ethnic groups on drug behaviors, except for marijuana use. HIV positive female IVDUs (excluding prostitutes) reported higher numbers of male sex partners. Female IVDUs who reported prostitution during the last 12 months were less likely to be HIV positive than those who did not. Educational and counseling interventions in methadone maintenance programs should focus on IVDUs using cocaine and heroin, poly-drug users, sexually active young female IVDUs, and IVDUs who are not using condoms, particularly among prostitutes. 6 tables and 26 references (Author abstract modified)