An inhibitor of human platelet aggregation was identified from the venom of an Australian Copperhead snake, Austrelaps superba, as a novel phospholipase A2. The inhibitor was purified to homogeneity by chromatography on Q-Sepharose, S-Sepharose and C8 reverse phase HPLC. The purified phospholipase A2 has a molecular weight of 15 kDa as assessed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). N-terminal sequence analysis of the platelet inhibitor revealed 70-80% sequence identity to other previously described secretory phospholipase A2. Phospholipase activity of the purified protein was confirmed by the ability of the enzyme to hydrolyse lecithin. Pretreatment of the purified protein with the specific phospholipase A2 inhibitor p-bromophenacyl bromide, resulted in abrogation of both its enzyme and platelet inhibitory activity. The phospholipase A2 inhibited platelet aggregation and serotonin release, induced by a variety of platelet agonists, in a time and dose dependent manner.