This study will evaluate hepatitis C virus (HCV) infection in blood donors who test positive for antibodies to this virus. Most HCV-infected people do not become ill and are not aware that they have hepatitis or have had it in the past. Some infected people recover completely, whereas others remain chronically infected. The study will try to define infectivity of anti-HCV positive individuals, routes of transmission of the virus, and the number of HCV-infected persons who have evidence of liver disease.

Blood donors at the NIH Clinical Center or the Central Maryland Chapter of the American Red Cross who test positive for HCV may be eligible for this study. Participants will have a physical examination and history, including questions about socioeconomic status and current sexual practices. They will have 100 milliliters (ml) (6 tablespoons) of blood drawn at the first visit and 50 ml (3 tablespoons) drawn 3, 6, 9 and 12 months after the initial visit. Some participants may undergo plasmapheresis, a procedure for collecting additional plasma (the liquid portion of the blood). For this procedure, whole blood is collected through a needle placed in an arm vein. The blood circulates through a machine that separates it into its components. The plasma is then removed, and the red and white cells and platelets are returned to the body, either through the same needle used to draw the blood or through a second needle placed in the other arm. In some individuals, other body fluids (saliva, urine or semen) may also be collected.

Participants may be asked to bring their household contacts and sexual partners to NIH for interview and blood testing for evidence of HCV infection and liver disease. Although this is not required for participation in the study, it would provide additional valuable information.

Participants found to have chronic viral infection will be seen more often and will provide additional blood samples for routine medical care. Further medical evaluation may include X-rays or liver scans and referral to a specialist for additional tests or therapy.

Ten people in this study will be recruited to participate in a secondary investigation to analyze changes in the level of HCV and the immune response to it, and to relate these changes to the degree of liver damage. In addition to blood collected for the primary study, participants in this investigation will have an additional 50 ml (3 tablespoons) of blood drawn from an arm vein every week for 10 weeks to measure levels of virus, ALT (a liver enzyme), and immune response.