Approximately 30% of HIV infected patients are co-infected with hepatitis C virus (HCV) which is now the leading co-morbid disease in co-infected individuals. The histologic severity and natural history of HCV has been reported to be accelerated in those co-infected with HIV. It is hypothesized that 1) the severity and progression of HCV disease is related to the immune competence of the individual, 2) immune restoration associated with HIV therapy may further accelerate the progression of HCV disease which may explain the marked increase in HCV related morbidity and mortality observed in recent years, and 3) the virologic response to anti-HCV treatment is directly related to the degree of immunologic competence. The specific aims of the proposal are: 1) To obtain, through multi-disciplinary didactic teaching, the necessary skills of clinical research design, data collection, data analysis, and biostatistical methods and 2) To study the impact of HIV disease on HCV, the effect of the immune function and immune restoration during HIV therapy on the natural history of HCV, and the efficacy of HCV treatment in HIV co-infection.