Conventional serologic methods of antigen or antibody detection are now widely applied for diagnosis of hepatitis viruses A, B, C, and D. Nucleic acid quantitation has become very useful for monitoring response to antiviral therapy in cases of hepatitis B and C. Special confirmatory testing of HCV serologies can be quite specific, but overall serologies for HCV lack sensitivity for early diagnosis. Thus HCV RNA detection may ultimately be the preferred method for HCV diagnosis and for screening blood donors. Unfortunately, HEV diagnosis may rest on the efforts of research laboratories for electron microscopy, Western blot, or nucleic acid detection.