Entecavir (Baraclude) is a novel nucleoside analogue of 2'-deoxyguanosine whose intracellular triphosphate form inhibits replication of the hepatitis B virus (HBV). In large, randomised, double-blind, phase III clinical trials in patients with chronic HBV infection, oral entecavir 0.5 or 1.0mg once daily for up to 96 weeks was superior to lamivudine 100 mg/day in improving hepatic histology, normalising aminotransferase levels and suppressing viraemia to levels undetectable by polymerase chain reaction (PCR) assay in nucleoside-naive hepatitis B e antigen (HBeAg)-negative (precore or core promoter mutants) and/or HBeAg-positive patients, and in lamivudine-refractory (persistent viraemia during lamivudine therapy) HBeAg-positive patients. In addition, the tolerability profile of entecavir was generally similar to that of lamivudine. Thus, entecavir is a primary option in the treatment of chronic HBV infection in both nucleoside-naive and lamivudine-refractory patients.