the corresponding tissue fed with normal diet, the enzyme activities of chymotrypsinogen, trypsinogen, amylase and lipase were depressed by 0-10%, 0-20%, 10-15% and 20-25% respectively at the end of two weeks during the feeding of group I and group II and then these range of depletion of enzyme activities maintained continuously up to the end of tour and six weeks. This result suggests that digestive enzyme activities are influenced by only depletion of protein but not by various amount of fat in diet at all when carbohydrate is sufficient. Some of animals in groups I and II receiving designated diet for four and six weeks were transferred to the normal diet then pancreatic enzyme were assayed on the third, fifth and seventh days. The recovery of these enzymes is remarkable, and apparently the rats fed protein-and lipid-depleted diet were able to respond immediately to the stimulus of diet. Complete recovery of chymotrypsinogen, trypsinogen and lipase was observed after three days feeding regardless rats fed with protein- and lipid-depleted diet for four or six weeks except amylase which was recovered after five days feeding in the group of rats fed diet I and II for four weeks and seven days feeding in the group of rats fed diet I and II for six weeks. No difference in the recovery rate of enzyme was observed between diets I and II and also between the group of the rats when the rats in groups I and II shifted to the normal diet at four weeks and six weeks. Rats fed protein- and lipid-depleted for four and six weeks were not able to respond to the stimulus of diet, at all, which consists of high lipid. low protein, and low carbohydrate. This result illustrates that the essential factor for stimulus of enzyme activity is protein in diet but not carbohydrate and fat. The effect of high proportion of fat to carbohydrate (94: 6) in isonitrogenous, isocaloric diet on pancreatic enznyme activities also was studied in rats and compared to the effect of normal isocaloric diet. The diet which provided 57 cal/day and the experiment lasted for four weeks, no effect of this diet on pancreatic chymotrypsinogen, trypsinogen and lipase was observed. However, pancreatic amylase was reduced to 61.5% at the end of three weeks and 64% at the end of four weeks. This result indicates that pancreatic amylase activity may be related when carbohydrate is restricted but protein is normal in diet. These results indicate that when various dietary composition is related to the pancreatic enzyme activity, one of main influential factor in diet on pancreatic enzyme is protein, but not fat at all. However pancreatic amylase acivity may be related when carbohydrate is resticted but protein is normal in diet. Our experimental evidence tends to indicate that enzyme synthesis in the pancreas is regulated, at least in part by the composition of amino acid pool(s) in the acinar cells of pancreas. This may be due to the decreased amount of amino acid in the dietary protein, but not composition of fat. It can be postulated that the decrease in the dietary protein affects synthesis and secretion of pancreatic digestive enzymes, and then the intracellular structure of the cell, resulting in decrease of cell activity and tissue debility.