The in vitro microsomal metabolism of the strain 13 quinea pig pancreas was investigated by determining benzo(a)pyrene (BP) hydroxylase activity in the 9000 .times. g supernatant and microsomal pellet. BP hydroxylase activity in the 9000 .times. g supernatant and microsomal pellet of the pancreas was < 1% of the activity in the respective liver fractions. Pretreatment of animals with methylcholanthrene or BP at 20 mg/kg, for 1 or 3 days, enhanced the BP hydroxylase activity of pancreatic microsomes over that of controls. The induction in the liver microsomes was less than 2-fold over that of controls. The hydroxylation of BP by pancreatic microsomes was linear with time over a 30 min period, with the rate of hydroxylation dependent on enzyme and substrate concentrations.