Significant purification of the ubiquitous cytochrome P-450-A and the strain-specific P-450-B from Drosophila melanogaster has been achieved by sequential chromatography on octylamino-agarose, DEAE-cellulose and hydroxyapatite. Preparations of P-450-A (specific contents of 7-9 nmol/mg) were homogeneous as determined by SDS/polyacrylamide-gel electrophoresis (PAGE) analysis. Preparations enriched for P-450-B (specific contents of 4-7 nmol/mg) contained significant amounts of P-450-A but were essentially free of other proteins as judged by SDS/PAGE. Partial reconstitution of 7-ethoxycoumarin de-ethylase activity was achieved using rabbit NADPH: cytochrome P450 reductase and purified preparations containing P450-B.