Aims. To assess risk factors associated with injection drug users (IDUs) who give injections to or receive injections from other IDUs. Design and setting. IDUs were recruited into a cross-sectional study using targeted sampling methods in Oakland, Richmond, and San Francisco, California from August 1996 to January 1997. "Street docs" are IDUs who reported having given injections to other IDUs in the past month. "Injection recipients" are IDUs who reported having received injections from other people in the past month. Participants. Of 1166 IDUs interviewed, 283 (24%) reported being injection recipients and 427 (37%) reported being street docs. Measurements. Socio-demographic characteristics and injection-related risk behaviors. Findings. Injection recipients and street docs were significantly more likely (p<0.001) than other IDUs to report sharing syringes (33% of injection recipients, 21% of street docs and 7% of others), cookers (71% of injection recipients, 55% of street docs and 24% of others), rinse water (44% of injection recipients, 35% of street docs and 13% of others), and filters (60% of injection recipients, 47% of street docs and 20% of others). In a logistic regression model, injection recipients (adjusted odds ratio (AOR) = 4.29) and street docs (AOR = 1.91) were more likely than other IDUs to report having shared syringes. Conclusions. Giving and receiving injections is common among IDUs in the San Francisco Bay area. Qualitative and epidemiological studies are needed to understand better the infectious disease risks associated with giving and receiving injections. Interventions need to address these issues and provide practical solutions.