Since the gene products (M1 and M2) of influenza virus RNA segment 7 have been implicated in host range restriction, sensitivity to the drug amantadine, virus yield in chicken embryos as well as in virus assembly and morphology, we have determined the nucleotide sequence of this RNA segment for an avian [A/FPV/Weybridge (H7N7)] and a human [A/WSN/33 (H1N1)] virus and compared it to that of the other influenza A virus strains. The results show that all ten strains of influenza A virus contain an identical number of nucleotides (1027 bases) in RNA segment 7 and an identical number of amino acids in M1 (252 aa) and M2 (97 aa) proteins. The observed amino acid changes are conservative in nature suggesting the requirement of a critical structure of both proteins in virus assembly. Furthermore, the presence of some consistent amino acid substitutions among different human and avian strains also supports the possible existence of host range and drug resistance determinants in M1 and M2 proteins.