The biotransformation capability of pancreatic tissue was studied. Michaelis-Menten kinetics were determined for glutathione S-transferase in pancreatic tissue supernatants from control, phenobarbital (PB), and 3-methylcholanthrene (3MCA)-pretreated Sprague-Dawley male rats. The enzyme activity was measured spectrophotometrically with use of 1-chloro-2,4-dinitrobenzene as substrate. Pancreatic activity was about half the hepatic activity, and, further, the activity was not affected by pretreatment with PB or 3MCA as was the liver.