The relationship between alcoholic liver disease and hepatitis C virus was studied in 80 patients by searching for hepatitis C virus RNA with the polymerase chain reaction and by measuring hepatitis C virus antibodies. By C-100 enzyme-linked immunosorbent assay, hepatitis C virus antibodies were found in 2 of 10 patients with fibrosteatosis, 8 of 20 patients with alcoholic hepatitis, 14 of 19 patients with chronic hepatitis and 19 of 31 patients with cirrhosis. Percentages of patients with antibodies found by C-100 radioimmunoassay and by enzyme-linked immunosorbent assay based on sequence peptide 42 were lower; of the 16 patients with a low titer by C-100 enzyme-linked immunosorbent assay, 10 were negative by radioimmunoassay and 6 were negative by sequence peptide 42. By a second-generation recombinant immunoblot assay, hepatitis C virus antibodies were found in 1 of 10 patients with fibrosteatosis, 2 of 20 patients with alcoholic hepatitis, 15 of 19 patients with chronic hepatitis and 18 of 31 patients with cirrhosis. Hepatitis C virus RNA was found in 1 of 10 patients with fibrosteatosis, 3 of 20 patients with alcoholic hepatitis, 13 of 19 patients with chronic hepatitis and 20 of 31 patients with cirrhosis. Of the 37 patients with hepatitis C virus RNA, 31 had antibodies by C-100 enzyme-linked immunosorbent assay (25 patients at a high titer [cut-off index greater than 6]), and 31 had antibodies by second-generation recombinant immunoblot assay. Patients with cirrhosis and hepatitis C virus RNA had higher ALT activity than such patients without hepatitis C virus RNA (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)