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.