RESUMEN
The discovery in migrating birds of influenzaviruses and the demonstration of relationships between strains found in man and in birds show the importance of these investigations for influenzavirus ecology. Investigation of birds in the far-east regions of the USSR is particularly important as many of them migrate to South-East Asia and China, the regions from which human influenza pandemics seem to originate. A total of 262 bird sera from these regions were titrated by the HI method with 20 different influenzavirus antigens (5 human, 2 equine, 1 swine, and 12 avian influenzaviruses). Haemagglutination-inhibiting activity was found in 16.8% of the tested sera, most frequently in sera of Anas formosa, Gallinago gallinago, Anas falcata, and Larus crassirostris. HI activity to A/turkey/Wisconsin/66 (Hav6N2) was found in 7.3% of the sera.