The overall goal of the proposed health services research project is to improve the outcome of medical care for injection drug users (IDUs) with Hepatitis C virus (HCV) infection. This will be done by testing two interventions designed to improve the rates of HCV treatment completion and sustained virologic response (SVR) in IDUs. The first will increase access by integrating HCV medical care into substance abuse treatment, and the second will use voucher incentives to reduce drug and alcohol use among IDUs with HCV infection. HCV infection is endemic among IDUs, and is associated with significant medical morbidity. While antiviral treatments are improving rapidly, providing HCV medical care for IDUs remains problematic for a number of reasons. IDUs often do not have adequate access to HCV diagnosis and treatment services, and they may engage in active drug and alcohol use, making them ineligible for treatment. Continued drug and alcohol use also worsens HCV outcomes by reducing adherence to HCV treatment and reducing the effectiveness of treatment. The proposed project is a five-year program of work made up of two controlled clinical trials, studying 220 patients with HCV infection enrolled in methadone maintenance treatment (MMT). Study 1 - Integrated HCV Medical Care - is a randomized trial to test the efficacy of On-site HCV Medical Care provided at the MMT program versus Off-site care at the GI Clinic. HCV antibody positive MMT patients will be randomly assigned to receive HCV medical services either through an integrated delivery model located on-site in the MMT clinic, or through usual off-site referral to the GI Clinic. The main outcomes will be the rates of attaining SVR and completion of HCV treatment, as well as other measures of HCV related health outcomes and quality of life. Study 2 - Voucher Incentives to Reduce Drug Alcohol Use - is a randomized trial of voucher-based incentives to reduce heroin, cocaine, and alcohol use and to thereby increase the rates of completion of HCV treatment and achieving SVR. Eighty HCV antibody positive MMT patients will be randomly assigned to one of two study conditions: a) Voucher group in which participants can earn vouchers with monetary value as incentives for drug and alcohol-free urine tests, and b) No Voucher control group. The main outcomes will be completion of HCV medical treatment, SVR and other HCV-related health measures, and quality of life. These studies are expected to yield new knowledge about the efficacy of providing on-site HVC medical care in substance abuse treatment programs. They will also provide information about how HCV treatment outcomes are affected by incentives to reduce drug/alcohol use in MMT patients with chronic HCV. Finally, the studies will also provide information about the influence of active drug and alcohol use on HCV medical outcomes such as treatment completion and SVR.