The clinical spectrum of hepatitis C is variable and the factors responsible for these divergent outcomes with chronic hepatitis C infection remain unknown. Dr. Fried and his colleagues are studying a cohort of hemophilic siblings infected with hepatitis C to define the natural history, immunologic, and genetic factors that influence its clinical outcome. Patients with hemophilia have a prevalence rate of hepatitis C as high as 90 percent. The sex-linked pattern of inheritance of hemophilia allows them to identify a cohort of siblings both of who have been infected with hepatitis C. Hemophilic siblings are an attractive population to study because: 1) They are all males; 2) Siblings are relatively close in age; 3) The mode of HCV acquisition is identical; 4) The age at acquisition of hepatitis C is similar 5) The date of acquisition can be confidently estimated upon their factor replacement history; 6) Hemophilic sibs share significant amounts of genetic material.