The authors studied, by the complement fixation test, the A2 influenza virus strains isolated from various brazilian localities, during the 1957 epidemic. They prepared immunesera in roosters by the inoculation of the infected allantoic fluid with each of the 17 isolated strains, in comparison with immunesera prepared with the PR8, Weiss, FM1, Japan and Lee strains. The tests were positive with the A group of antigens and negative with the B type, Lee strain. The tests performed with the A2 virus antigen fixed complement to a titer 8 to 16 times higher than the A and A1 virus antigens. The behavior of those 17 strains and the Japan strain was the same.