Phospholipase A2-I (PLA2-I) was isolated from Agkistrodon bilineatus venom by Nikai (Nikai et al., 1993). The amino acid sequence of the phospholipase A2-I was determined by the Edman sequencing procedure of peptides derived from digests utilizing cyanogen bromide, clostripain, metalloendopeptidase, chymotrypsin, and Staphylococcus aureus V8 protease. In the reduced state, purified phospholipase A2's molecular weight was determined to be 14,000 as demonstrated by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Purified PLA2-I also contained 1 mol of Ca per mol of protein and consists of 123 amino acid residues resulting in a calculated molecular weight of 14,133. Both phospholipase and lethal activities were found to be inhibited by bromophenacyl bromide, suggesting that the histidine residue is involved in this activity. Also there was an increase in the creatine kinase activity of mice serum, which is an indicator that PLA2-I is involved in muscle damage.