The rapidly emerging and sometimes complicated field of HCV diagnostics can be simplified by classification of tests into two general categories: serologic tests which screen for anti-HCV antibodies, and molecular tests which are used to assess HCV viremia and characterize viral infection at the genetic level. Antibody tests include the highly sensitive screening enzyme immunoassays (current versions: EIA-2 and EIA-3), and supplemental tests such as the recombinant immunoblot assay (RIBA-2). Molecular assays such as HCV RNA polymerase chain reaction (PCR) may play an important role in confirming HCV infection in several clinical situations, such as immunosuppressed patients with chronic hepatitis C, patients with acute hepatitis who might be in the diagnostic "window" period prior to seroconversion, and seropositive patients with normal ALT values. Quantitative HCV-RNA tests, such as quantitative PCR (Q-PCR) and branched DNA (bDNA), provide valuable tools for assessing the level of HCV viremia prior to and during therapy. Genotype tests allow classification of HCV infection in one of six distinct HCV genotypes, although the clinical relevance of HCV genotype tests has not been established.