A new myotoxic phospholipase A2 homologue, having a serine residue in position 49 instead of highly conserved aspartic acid, was found in the venom of Vipera ammodytes. The primary structure revealed additional mutations in the positions important for enzymatic activity. Tyr28 is exchanged for a histidine and Gly33 for asparagine. These changes render earlier-reported weak enzymatic activity unlikely. The role of this rather abundant venom fraction is apparently in myotoxicity, which was confirmed in the muscle-cell culture from neonatal rats. The muscle-cell culture proved to be a good tool to investigate the effects of various myotoxins on muscle cells.