The protein-A gold method using specific rabbit sera directed against pure human pancreatic chymotrypsinogen and carboxylic ester hydrolase was applied to locate these (pro)enzymes in human pancreatic acinar cells and intestinal Paneth cells. Quantitative evaluation of the labelling indicated that both (pro)enzymes are present in pancreatic acinar secretory granules. In Paneth cell secretory granules, only carboxylic ester hydrolase was present in significant amounts, although the labelling for this enzyme was less intense than that observed in pancreatic zymogen granules. The results obtained support the view that Paneth cells represent a "diffuse exocrine gland" scattered along the intestine, whose role is either to act as a substitute in the event of a deficient pancreas or to regulate the intestinal flora.