Intravenous (IV) drug abusers are at risk for contracting transmittable diseases such as acquired immunodeficiency syndrome (AIDS) and hepatitis B. This study was conducted to investigate the prevalence of risk behaviors for acquiring and transmitting AIDS and hepatitis B among treatment-seeking drug abusers (N=168). Subjects participated in a structured interview conducted by a clinical psychologist and a drug counselor which focused on drug use, needle sharing, and sexual behavior. Exposure to disease was assessed by testing blood samples. The majority of the subjects reported intravenous drug use; 65% of IV users reported needle sharing during the past year. Sharing was restricted to three or fewer people by the majority of sharers, and sharing often took place in places where users were less likely to share with a stranger. Significantly, 17.6% of subjects reported ceasing needle sharing over one year ago, suggesting that drug abusers can modify their health risk behaviors. Subjects reported few sexual partners and minimal homosexual contact. Only one blood sample tested positive for AIDS, perhaps due to the subjects' selectivity in sharing and their limited mobility. Thirty-one percent of the samples tested positive for current or past hepatitis B exposure. Educating drug abusers in treatment programs may result in dissemination of critical information about transmittable diseases to other drug abusers. (NB)