Abstract
1. Xanthine enzyme system in lepidopterous insects was demonstrated to be dehydrogenase but not oxidase.
2. The enzyme activity was high in the fat body and Malpighian tube, but was low in the mid-gut wall, whereas it was negligible in the rectum, integument and blood.
3. In the Periplanela americana, the enzyme activity was found in the Malpighian tube, fat body, hind-gut wall and mid-gut wall, but not in for-gut wall.
