There are 3 drugs registered to treatment of chronic hepatitis B: interferon, lamivudine and adefovir. Many other nucleoside and nucleotide analougs are examined. In experiments on the animals: woodchucks infected with WHBV and ducks infected with DHBV beneficial influence of entecavir on viral DNA and cccDNA supression. In these examination no resistance was present. In clinical studies resistanse to entecavir conserned only patients with resistance to lamivudine. Entecavir is safety and effective in the treatment of chronic hepatits B in patients HBeAg positive and negative and in patients with resistance to lamivudine.