Various subtypes of avian influenza viruses caused more or less extensive lethal epidemics before, affected especially gallinaceous domestic fowls. At the presem time it is divided into the less pathogenic (LPAI) flu, when a part of the sick birds survive and the highly pathogenic (HPAI) flu such as A H7N7 and A H5N1, with the invariably fatal outcome. In mass infections of the poultry, there were occasionally sick persons, who were in close contact with the sick birds. Panzootic caused by the A H5N1 subtype, which increased its pathogenicity through drift changes, resulted in death of more tlian 100 millions of poultry. It surpassed the species barrier and caused fatal infections in other species of birds, some mammals, but severe or even fatal diseases in ten of human individuals. The transfer of infection from the sick human individuals to per¬sons in their neighborhood was not observed. Inhibitors of neuraminidases proved to be efficient therapeu-tic drugs in the first two days of infection with avian influenza. In pandemie should oceur, decisive preven-tion measurc would be anti-flu vaccine prepared from the pandemie virus.

        Key words: LPAI - HPAI - pandemie - neuraminidase inhibitors - vaccine