Oxidation rates of alkylbenzenes have been measured in 10000g supernatants of vertebrate livers, locust fat bodies and housefly abdomens. 2. Activity per g. of insect was greater in fly than locust preparations but both were of the same order as a range of vertebrate species. 3. Methyl groups of toluene and p-nitrotoluene were oxidized more rapidly than the side chains of higher homologues. 4. In the higher homologues hydroxylation occurred most readily at the alpha-methylene group and less readily at penultimate methylene and terminal methyl groups. 5. Oxidations in both vertebrates and insects were inhibited by piperonylbutoxide and similar synergists. 6. Oxidation activity was stimulated by pretreatment of rats, but not locusts, with phenobarbitone or 3,4-benzopyrene.
