A lethal myotoxin, named mulgotoxin a, was isolated from the venom of the Australian king brown snake ( Pseudechis australis) by chromatography on Biorex 70 and SP-Sephadex ion exchange resins. Mulgotoxin a was obtained from one of four lethal fractions which were present in the venom. Mulgotoxin a is a basic toxin consisting of a single polypeptide chain of 122 amino acid residues cross-linked by seven disulphide bridges. Its N-and C-terminal residues are aspartic acid and leucine respectively. Mulgotoxin a causes myoglobinuria in mice and has an approximate ld 50 of 200 μg/kg body weight (mice). Its activity appears to be specific for skeletal muscle, causing massive cell damage both in vivo and in vitro.