Full-length DNA copies of M-gene of remantadine-sensitive and remantadine-resistant variants of the influenza virus strain A/FPV/Weybridge (H7N7) have been synthesised and cloned. Complete nucleotide sequences of both cDNAs were determined by the Maxam-Gilbert method. There are three nucleotide substitutions, two of which lead to amino acid changes in M1 and M2 proteins. The existence of M3 protein, a polypeptide 68 amino acids long, encoded by the negative strand of RNA, is suggested. Amino acid changes in M2 and M3 proteins and their relation to the remantadine resistance are discussed.