<p>The problem of predicting a culprit of the future influenza pandemic is analyzed in connection with the emerged epizootic of cows caused by the avian influenza H5N1 strain. The emerged epizootic in cows is considered as acquisition of a new host by the H5N1 virus. The reproductive cycle of the H5N1 virus is adapted to a high temperature. In cows, the body temperature varies and is closer to the body temperature in birds than in human. The H5N1 virus nucleoprotein is distinguished by a high content of arginine and lysine, which causes the optimum of viral replication and transcription at elevated host body temperature. In this aspect, the acquisition of cows (but not human) as a host by the H5N1 virus is more optimal. Another peculiarity of the H5N1 virus, which excludes the possibilities of its transmission into the human population, is associated with the peculiarities of its internal proteins (particularly, with a biomarker of influenza virus pandemicity). The invariance matrices of all primary structures of internal proteins of the H5N1 virus differ significantly from those in the strains of influenza pandemics in 1918, 1957, 1968, and 2009, which also does not support the prediction about the H5N1 virus as a herald of a future influenza pandemic. <b>Conclusions</b>. Based on the history of the emergence of last four influenza pandemics and comparison of biological properties and molecular characteristics of hemagglutinins of influenza viruses of the H1N1 and H3N2 subtypes, the H1N1 virus subtype is assumed to be the most likely causative agent of a future influenza pandemic.</p>