L-amino acid oxidase (E.C. 22.214.171.124) was purified from the venom of Bothrops asper snakes from Costa Rica. Three forms of this enzyme were obtained from the crude venom using only two steps: heating in the presence of L-leucine and chromatography on DEAE-cellulose. The isozymes were numbered 1, 2a and 2b on the basis of electrophoretic mobility towards the anode. Isozymes 1 and 2b were homogeneous by acrylamide gel electrophoresis and sedimentation velocity. They showed a molecular weight of 125,000 by sedimentation equilibrium.