The virological diagnosis of viral hepatitis is based on the study of direct markers (viral antigens and genomes) and indirect markers (specific antibodies). The diagnosis of hepatitis B is based on the interpretation of antigen-antibody profiles and, for chronic hepatitis B, on HBV DNA detection. Treatment responses are assessed by the HBe seroconversion in HBe antigen-positive patients, and by measuring HBV DNA levels. The diagnosis of hepatitis C is based on the detection of anti-HCV antibodies and HCV RNA by means of molecular techniques. HCV genotype determination is used to tailor the treatment schedule to the individual patient. Treatment efficacy is assessed by means of molecular techniques to prove progressive and definitive viral clearance.