Abstract
1. Homogenates of insect tissues were assayed for enzymes capable of oxidizing p-nitrotoluene to p-nitrobenzoic acid. 2. Locust fat-body homogenate 10000g supernatant was an effective enzyme and required no added cofactors. 3. Homogenates of other insects or locust organs and 10000g sediment from locust fat-body were not active and inhibited microsomal oxidations carried out by locust fat-body or rabbit liver enzyme. 4. Inhibitory power was high in homogenates of whole flies and of fly heads or thoraces. 5. Inhibition appeared to involve both irreversible inactivation of enzyme and the removal of essential cofactors.