We compared the sociodemographic, drug use, and social support characteristics of injection drug users (IDUs) who reported at least 6 months having not "shared needles or works" (zero sharing risk) with those who reported recent equipment sharing. 187 AUDIT-positive (> 8), active IDUs were recruited between February 1998 and October 1999 from a needle exchange program in Providence, RI. The sample was 64% male and 87% white, with a mean age of 36 years, and 32% of subjects reported zero sharing risk in the prior 6 months. Variables having significant (P < .05) associations with zero sharing risk included: older age, lower heroin use frequency, lower cocaine use, and increased frequency of needle exchange visits. As social support from friends increased, the likelihood of sharing decreased. Subjects with.. substance-using friends or partners were significantly more likely to share than those without such associations (OR = 9.4; P < .05). Social support and social network composition influenced sharing behaviors in active, out-of-treatment drug injectors. Interventions that mobilize social support may increase the possibility of zero sharing, an important public health goal. (C) 2002 Elsevier Science Inc. All rights reserved.