The purpose of this study is to determine the efficacy of a peer-volunteer intervention to reduce high-risk transmission behaviors among hepatitis C virus (HCV)-infected young adult injection drug users (IDUs), and to identify the proportion of these individuals who would be eligible and willing to undergo treatment to eradicate HCV infection. HCV is one of the most frequently occurring human viral infections, having an estimated worldwide prevalence of 3%. In many regions of the United States, between 65% and 95% of IDUs are HCV-seropositive and capable of transmitting the infection. To date, research studies targeting infected individuals to prevent secondary transmission of chronic blood-borne viral infection have generally been limited to post-test counseling and case management. In addition, recent data suggest that medical treatment of HCV infection may be most effective when offered soon after HCV seroconversion. However, the proportion of HCV-infected IDUs who meet strict national guidelines for HCV treatment is likely to be small because treatment is usually postponed while drug use continues. Determining the proportion of infected individuals who may be both eligible and willing to undergo HCV therapy is highly important for guiding national standards and objectives to achieve greater numbers of IDUs in HCV therapy. We have previously reported that fewer than 1% of HCV-infected IDUs in Baltimore are currently receiving such therapy. Early initiation of HCV treatment among young IDUs in conjunction with a reduction in HCV transmission risk behaviors may ultimately lead to a reduction in incident HCV infection at the individual and the community levels.