As indicators to determine the diagnosis, condition, and prognosis of hepatitis C, methods have been developed such as the detection of HCV-RNA by the nested RT-PCR method, quantitative assay of HCV-RNA by the competitive RT-PCR method, qualitative and quantitative assay of various anti-HCV IgG and IgM antibodies, and identification of viral type (genotype and serological group). The clinical utility of these HCV markers in early diagnosis and prognosis of acute hepatitis C, for differentiating it from acute flare in HCV carriers, and in distinguishing between past and current infection in second-generation-anti-HCV-positive patients with normal serum alanine aminotransferase has been evaluated.