The course and outcome of hepatitis C virus (HCV) infection is determined by both host and viral factors, none of which have been well defined. In this study, we will follow and assess patients who are occupationally exposed to HCV for viral and immunologic factors that may relate to disease outcome. This protocol is mostly a sample acquisition protocol to support laboratory research. Patients will be interviewed and have blood (and lymphocytes) taken as soon as possible after exposure and again after 2, 4, 6, 12, 24 and 48 weeks. Virological markers, serum antibodies and both CD4 and CD8 T cell responses to HCV will be monitored. Persons who develop hepatitis C will be referred for therapy or enrolled in therapeutic trials currently in place at the National Institutes of Health. These studies will help define the relative roles of virological and immunological factors in determining the course and outcome of HCV infection.