In a cohort of 483 blood donors positive for antibody to hepatitis C virus on second-generation enzyme-linked immunosorbent, the confirmatory second-generation recombinant immunoblot assay (Ortho Diagnostic Systems) was positive in 172 cases (36%), indeterminate in 113 (23%), and negative in 198 (41%). We further studied 94 of the donors (recombinant immunoblot assay positive in 85, indeterminate in 6, and negative in 3). Alanine transaminase (ALT) activity, assayed on three occasions, was elevated in at least one assay in 85% of the 85 recombinant immunoblot assay-positive donors. Liver disease was present in 95% of these patients (chronic persistent hepatitis, 35%; chronic active hepatitis, 53%; cirrhosis, 7%). Ten of the 13 recombinant immunoblot assay-positive donors with normal ALT activity had liver disease; polymerase chain reaction testing for viral RNA was predictive of liver disease in most cases. Donors with cirrhosis differed significantly from cirrhosis-free donors in terms of age, sex ratio, ALT activity, and excessive alcohol consumption. Three of the 6 recombinant immunoblot assay-indeterminate donors (isolated C 22) who underwent histological examination had elevated ALT activity and liver disease. The 3 recombinant immunoblot assay-negative donors evaluated were free of liver disease. This study shows that anti-HCV second-generation enzyme-linked immunosorbent positivity is confirmed in fewer than 40% of blood donors by the second-generation recombinant immunoblot assay, and that liver disease is present in 95% of recombinant immunoblot assay-positive donors. Recombinant immunoblot assay positivity combined with viremia is frequently associated with the existence of liver disease, regardless of transaminase activity. Excessive alcohol consumption may be an important factor in the onset of cirrhosis in anti-HCV-positive blood donors.