The activities of amylase, lipase, phospholipase, and trypsin in four commercially available preparations of pancreatin with different galenic and adjunctive protective properties were estimated in vitro, using human small-intestinal juice as the incubation medium. These preparations were administered to healthy subjects and to patients with severe pancreatic insufficiency, and their ability to increase the intestinal concentrations of pancreatic enzymes was evaluated. The relations between in vitro and in vivo activities were also studied. In vitro testing showed that the preparations contained high but varying activities of enzymes, with the greatest variations in lipase and trypsin. Pancreatin in the form of tablets, with or without protective measures against acid, did not cause any apparent increase in the activities of pancreatic enzymes in the upper part of the gut in patients with pancreatic insufficiency. Granulated pancreatin, on the other hand, brought about an increase in the activities of amylase, phospholipase, lipase, and trypsin. Relatively higher activities of the enzymes in granulated form reached the small intestine as compared with those of the tablets.