This study compared the baseline sociodemographic characteristics and HIV risk behaviors of two groups of out-of-treatment injection drug users (IDUs): 366 who concurrently smoked crack (smoking IDUs) and 212 who did not smoke crack (IDUs) in the past 30 days. Temporal trends in recent risk behaviors were also assessed for each drug user group over an 18-month period, January 1992 through June 1994. Baseline data were collected in South Philadelphia before the implementation of a multisite HIV intervention research project funded by the National Institute on Drug Abuse. For the temporal trend analysis, the sample was grouped into four intake periods based on the date of the baseline interview. The results indicated that although both groups were economically disadvantaged and at high risk of HIV infection and transmission, smoking injectors had fewer economic resources and were at a moderately greater risk because of higher levels of sexual risk behaviors. Analysis of temporal trends revealed few reductions in drug risk behaviors and none in sexual risk behaviors. This study points to the need for examining differences between types of drug users, developing appropriate multidrug treatment programs and assessing the characteristics of communities so that theory-based interventions can be tailored for maximum effectiveness.