The nutritional effects of feeding raw and heated soy flour to young golden Syrian hamsters were investigated over a period of 32 days. Those animals fed raw soy flour grew much more poorly than those fed heated soy flour, an effect which was reflected in a lower food efficiency as well. Growth retardation of hamsters fed raw soy flour was accompanied by a lower apparent digestibility of the protein (54%) compared to heated soy flour (76%). The pancreases of animals fed raw soy flour were increased in size and had elevated levels of trypsin, chymotrypsin, amylase, and lipase. With the exception of trypsin activity in the small intestine, similar differences in enzyme activities between the raw and heated soy groups were generally found in the small intestine, cecum, large intestine, and feces. There was, however, a progressive decrease in these activities in the lower regions of the intestinal tract and feces. It is concluded that the hamster, in common with several other species of animals, is sensitive to the effects of the trypsin inhibitors in raw soy flour, and may provide a useful model for studying the long-term effects of trypsin inhibitors on the pancreas.