Infection with hepatitis C virus (HCV) was analyzed by an enzyme-linked immunosorbent assay based on recombinant viral proteins encoded by regions of the putative viral core, NS3, NS4 and NS5, which were expressed in E. coli. Results showed that 106 of 124 cases (85.5%) of non-A, non-B chronic hepatitis and 43 of 45 cases (95.5%) of hepatocellular carcinoma, negative for HBV marker, were positive for antibodies against at least one of these viral proteins. One of 87 healthy individuals with normal alanine aminotransferase activity was positive for antibody against only the viral core, but was negative for HCV RNA. The serum of one patient with chronic hepatitis was positive for one of these proteins, but negative for HCV RNA. These findings in combination with results on detection of HCV RNA in the sera of patients with non-A, non-B chronic hepatitis indicated that 105 of 124 cases (84.6%) were positive for HCV infection. Sera that were negative for HCV antibodies against all these proteins were also negative for HCV RNA assayed by reverse transcription followed by the polymerase chain reaction. Screening of HCV infection by detecting viral antibodies in circulating blood using all these viral proteins is useful for reducing the number of ambiguous results in screening for viral infection. Thus, this assay system may be useful diagnostic purposes.