The enzyme content and the ultrastructure of the rat exocrine pancreas were studied after feeding a normal diet or diets containing raw (RSF) or heat-inactivated (HSF) soybean flour for 20 days. The wet weight of the pancreas of RSF-fed rats was double that of HSF-fed animals. The protein concentration and total protein content of the pancreas of RSF-treated animals was significantly greater than in HSF rats. The increased protein content comprised parallel increase of enzyme and non-enzymic proteins, since the specific activities of amylase, trypsin and lipase were not significantly different between RSF- and HSF-fed rats. Increase in the number of zymogen granules in RSF-fed rats was the only significant ultrastructural difference from normal and HSF-fed rats, both before and after stimulation with cholecystokinin and secretin.