Summary The primary structure of cytotoxin VII4, consisting of 60 amino acid residues cross-linked by four disulphide bridges, was determined. Cytotoxin VII4 differs in altogether 17 residue positions from the other cytotoxins of the same snake. Comparing the amino acid sequence of cytotoxin VII4 from Naja mossambica mossambica venom to the known sequences of cytotoxins from the genera Naja and Haemachatus , 33 residues, including 8 half cystines, are identical. The amino acid sequence of cytotoxins as a group has 11 residue positions in common with the amino acid sequence of neurotoxins and based on this observation, 8 residues in the primary structure of cytotoxins could be implicated as probably being functionally important.