1. One reason, based on indirect evidence, advanced in explanation of the low nutritional value of raw soya bean (RS) is that it stimulates the pancreas to secrete massive amounts of protein which are ultimately lost in the faeces. This theory has been investigated directly.
2. The expected outpouring of pancreatic protein did not occur when the secretion of enzymes and protein in pancreatic juice from chickens and rats given successively heated soya bean (HS) and RS diets was measured directly.
3. It is suggested that RS, acting upon intestinal proteins, forms trypsin inhibitor-protein complexes which, in spite of adequate proteolytic activity, escape digestion and are lost with the faeces, thus decreasing the nutritional value of the diet.