Technical Abstract: Methods of microsome preparation were evaluated to determine their influence on the activity of cytochrome P450 monooxygenases in adult males and final instar nymphs of the German cockroach, Blattella germanica (L.). Aldrin epoxidase activity was significantly improved when homogenization occurred in a protected buffer and when alimentary canal contents were removed prior to homogenization. Apparently, a potent inhibitor of cytochrome P450 monooxygenases, but not of cytochrome c reductase, is present in the gut contents of German cockroaches. Aldrin epoxidase and methoxyresorufin (MR) O-demethyla midgut, hindgut, Malpighian tubules, fat body, and the remaining tissues of the carcass) from adult males and final instar nymphs. Adult male aldrin epoxidase activity was highest in midgut and Malpighian tubules, while no single tissue dominated in MR O-demethylase ac cspecific activity was 9- to 11-fold higher in midgut than in fat body, while MR O-demethylase specific activity was 17- to 22-fold higher in fat body than in midgut. In the final instar, aldrin epoxidase, MR O-demethylase, ethoxyresorufin (ER) O-deethylase, and cytochrome c reductase activities were lowest at the time of ecdysis and highest near the middle of the stadium. Dietary phenobarbital at the 0.2% level induced various microsomal oxidases including aldrin epoxidase, MR O-demethylase, ER O-deethylase, and cytochrome c reductase in final instar nymphs and adults.