Factors influencing the effectivity of replacement therapy with Panpur and Creon were controlled by in vivo and in vitro investigations. Both enteric coated preparations were equally acid protected, they even seemed to be more effective in hyperacid than in anacid chronic pancreatitis patients. Thus the uneven results of Panpur treatment in pancreatic steatorrhea cannot be explained by acid inactivation of the enzymes. Creon dose-dependently ameliorated the steatorrhea as well as vitamin B12 absorption while crushed but not the intact Panpur has only some insignificant effect. Good mixing of pancreatin with the B12-intrinsic factor - R protein complex and with the protein containing meal seems to be important for digestion of protein as well as fat. Unbound, overflowing trypsin activity of Panpur resulted in fast proteolytic inactivation of lipase. This could be diminished by soybean trypsin inhibitor which increased the in vivo effectiveness of the preparate. In summary Creon fulfilled two important factors of replacement therapy more successfully than Panpur: good mixing with meals and stability of lipase against proteolytic splitting, that is why it proved to be more effective for replacement therapy of pancreatic insufficiency.