The toxic phospholipase, pseudexin, was purified from the venom of the Australian red-bellied black snake, P. porphyriacus, and the sequence of the 15 N-terminal amino acids determined by automated sequence analysis. Pseudexin is composed of two isoenzymes with heterogeneity being observed at positions three and six. The sequence of the N-terminal portion of the two isoenzymes is: (Formula: see text).