In vitro and in vivo studies revealed that pancreases of Long-Evans male rats metabolized 3-methylcholanthrene (3MC) principally at the 1- and 2-carbon positions. The pancreatic metabolizing capability was not induced by pretreatment with either benzo(a)pyrene (BP) or phenobarbital (PB). During the period of observation from 5 to 48 hr, the maximum tissue content of radioactivity observed in the in vivo studies occurred at 16 hr after injection of 3MC in both liver and pancreas. Pancreatic tissue retained about four times more carcinogen per gram of tissue than liver tissues at all time periods.