Forty five blood donors with increased serum aminotransferases levels had liver histologic assessment and were tested for antibodies to hepatitis C virus (anti-HCV) with second and third generation ELISAs and RIBAs, and for HCV RNA with polymerase chain reaction (PCR) in serum and liver tissue. Twenty-nine of these 45 donors (65%) had steatosis without chronic hepatitis. Sixteen (35%) had chronic hepatitis. Twelve had evidence of HCV infection. Four had no evidence of HCV infection demonstrable by ELISA, RIBA or PCR. These four patients had no known cause of chronic hepatitis and no risk factor for parenterally acquired viral infection was found in them. This observation supports the hypothesis that a non-B, non-C virus might be implicated in chronic hepatitis. However, this hypothesis remains to be demonstrated.