The extent of involvement of hepatitis C, as compared to hepatitis A and hepatitis B, virus infection in acute and chronic liver disease in the Asir Region, southwestern Saudi Arabia, was assessed in 898 patients hospitalized during the period from June 1990 to November 1991. Acute icteric hepatitis cases with severe onset were distinguished by their referral to the fever hospital while cases with milder onset and those with chronic hepatitis were followed at two general hospitals. Antibodies to the c-100-3 antigen of hepatitis C virus (anti HCV) were detected in a significant proportion of patients with chronic liver disease (chronic active hepatitis (65%), cirrhosis (44%)). Anti HCV was also detected in patients with acute hepatitis with milder onset at the general hospitals (10.9%) but proportionately much less in patients at the fever referral hospital (< 1%) where hepatitis A (52%) and, to a lesser extent hepatitis B (11%), were mostly diagnosed. These results indicate that HCV is a major identifiable infection in hospitalized patients with chronic liver disease in this region but that anti HCV antibodies (c-100-3) are not detected, at least at onset, in sporadic cases with acute manifestations. Testing for additional viral antigens or RNA and a longer follow-up period would be required before exclusion of a role for HCV in acute disease. Alternatively, other viral and non-viral agents may be sought in this illness.