An epoxide hydrolase was solubilized with Cutscum® from microsomal fractions of southern army worm (Spodoptera eridania, Cramer) larval midguts. A 27-fold purification was achieved in high overall yield (38%) using ammonium sulphate fractionation, affinity chromatography (agarose with the ligand trans-9,10-epoxyoctadecanoic acid) and ion-exchange (DE-52) chromatography. The enzyme was judged highly pure by SDS-polyacrylamide gel electrophoresis and Ouchterlony double-diffusion analysis. The purified enzyme hydrolized styrene oxide and 1,2-epoxyoctane at the rates of 7.1 and 17.2 μmoles/mg protein/min respectively. Midgut epoxide hydrolase levels increased five-fold in specific activity and ninefold in total content during early development of the sixth larval instar and rapidly decreased at the onset of pupation. Hydrolase activity was enhanced two-fold following dietary exposure of the larvae to the mixed-function oxidase inducing agent pentamethylbenzene.