We investigated anti-hepatitis C virus (HCV) titers, HCV RNA levels in liver and serum, genetic variability in the hypervariable region of the genome, the form of the virus in the circulation, and liver histology in 21 anti-HCV-positive subjects with sustained normal liver biochemical values. Titer of anti-HCV was determined by second generation anti-HCV-passive hemagglutination assay, and HCV RNA levels were semiquantitated by reverse transcriptase polymerase chain reaction (PCR). In 19 (90%) of the 21 subjects who had a higher titer of anti-HCV (> or = 2(14)), HCV RNA was detected in both serum and liver, and histological examination showed minimal or mild chronic hepatitis in all. In the remaining 2 patients who had a lower titer of anti-HCV, HCV RNA was not detected in serum and liver, and liver histology was normal. Anti-HCV titers and HCV RNA levels in serum and liver in the 19 HCV RNA-positive subjects were compared with those levels in the 41 patients with biopsy-proven chronic hepatitis C and elevated serum aminotransferase levels as a control group. There were no significant differences in viral levels in serum and liver between the two groups. To further investigate virological differences between the two groups with regard to degree of genetic variability and the form in the circulation, we performed the PCR-single strand conformation polymorphism (PCR-SSCP) of the hypervariable region 1 and the immunoprecipitation analyses.(ABSTRACT TRUNCATED AT 250 WORDS)