A hemorrhagic toxin, designated Elegatoxin, was isolated from the venom of Trimeresurus elegans using HW-55, DEAE-Sephacel, CM-Cellulose and Mono S column chromatographies. The purified toxin was shown to be homogeneous by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, isoelectric electrophoresis, and Ouchterlony immunodiffusion. Elegatoxin has a molecular weight of 26,000 with an isoelectric point of 8.6. The toxin demonstrated both hemorrhagic and proteolytic activities. Hemorrhagic activity was inhibited by ethylenediaminetetraacetic acid (EDTA), ethyleneglycol-bis-(2-amino-ethylether)N,N'-tetraacetic acid (EGTA), o-phenanthroline, and N-bromosuccinimide, but not by amidinophenylmethanesulfonyl fluoride hydrochloride (APMSF). The minimum hemorrhagic dose was found to be 0.8 microgram/mouse. Elegatoxin possesses proteolytic activity as evidenced by hydrolyzing type IV collagen, actin and the A alpha, B beta, and gamma chains of bovine fibrinogen. This purified toxin contains 1 mol of zinc and 2 mols of calcium per mol of protein and a partial amino acid sequence was determined. The pathological and biochemical properties of Elegatoxin were investigated, and these results are reported in this paper.