Biological tests are important for the diagnosis and the follow-up of viral chronic hepatitis. The viral hepatitis C is by far the most frequent. The etiologic diagnosis is based on serological or immunological tests which have good sensitivity and specificity, and may be completed by molecular biological methods. In contrast, the tests for the evaluation of the activity (necrosis and inflammation) and of the fibrosis are less informative than the histological study. The diagnosis and prognosis interpretation of the aminotransferases are well known, but other tests as alpha glutathione S-transferase or orosomucoid are also proposed for evaluation of the activity. Some parameters as PIIINP or hyaluronic acid may be useful in the diagnosis and follow-up of fibrogenesis, fibrosis and cirrhosis but some new molecules, as the metalloproteinases and their inhibitors, are presenting interesting future prospects. Biological tests also contribute to the diagnosis of an associated extra-hepatic pathology and of a possible hepatocellular carcinoma occurring on the cirrhotic liver.