The two types of behavior important in examining the problem of AIDS among IV drug users are the sharing of contaminated injection equipment and sexual behaviors known to transmit HIV. After examining these two types of behaviors, the chapter considers risk reduction among IV drug users. It traces the history of studies which show that IV drug users are capable of changing their high-risk behaviors, summarizes the current state of knowledge about risk reduction among IV drug users, and suggests directions for future research. Recommendations for reducing risky behavior among IV drug users are that the appropriate government authorities provide drug treatment upon request for IV drug users throughout the county and sustain and expand current programs that provide for 'safer injection' to reach all current IV drug users. A discussion of research on IV drug use addresses research traditions, methods for investigating risky drug behaviors, and improving data quality. The study concludes with a discussion of estimates of the number of IV drug users and the rates of seroprevalence among them. 255-item bibliography.