Infection with the hepatitis B virus has switched over the last 20 years from the classical HBeAg positive serologic pattern to a HBeAg negative form that is linked, in the Mediterranean basin, with the epidemiologic replacement of the causative wild-type of virus B with mutant variants, whereby mutations in the core-promoter and in the pre-core region prevent the secretion of HBeAg. The wild-type pattern of infection (characterized by relatively high steady level ALT, high HBV-DNA levels and clinically overt liver disease) responds relatively well to Interferon: 3 to 5 mega units daily or 10 mega units every other day for 16 weeks induce anti-HBe seroconv ersion, normalize the ALT and possibly also eliminate the HBsAg in some 40% of the adults with a minimal (7%) risk of relapse. However, the mutant type infection (anti-HBe positive / HBe Ag negative) is less responsive to Interferon; this has led to the search for novel nucleoside analogues which has currently culminated in the advent of Lamivudine. This competitor of cytidine is 80% bioavailable and devoid of side-effects at the oral dose of 100 mg daily; tolerance continues for therapies up to 3 years. Lamivudine therapy shares with Interferon a rapid decline of ALT accompanied by improvement of histology; at variance with Interferon there is a delayed accumulating seronconversion to anti-HBe and the switch to anti-HBs is rare. Over the long term its activity is abolished by the emergence of specific viral mutations (YMDD mutants) that rekindle the disease. The indications to Lamivudine therapy in HBeAg negative chronic hepatitis B are currently under investigation. Lamivudine is highly efficacious in preventing HBV reinfection in liver transplants.