Investigations for the proof of isoenzymes of the alkaline phosphatase and the alpha-amylase in stool were carried out. The measurements of the faecal enzyme activities were performed in 96 patients with intestinal diseases. The disc electrophoresis in the polyacrylamide gel served for the separation of isoenzymes. The separated enzyme bands of the extracts of stool were compared with those ones of serum duodenal juice and extracts of the mucous membrane of the duodenum, the jujunum, the ileum as well as of the colon. Hereby up to 4 very much anodically wandering bands were present, which might be subunits or fission products of the alkaline phosphatase. In the alpha-amylase up to 5 bands could be proved, which were compared with those ones of the serum, the duodenal juice and the urine. A coordination of these isoenzymes concerning their origin is not possible. The faecal activities of enzymes correlate with the weights of stool. In exocrine pancreatic insufficiency and ulcerous colitis increased faecal activities of enzymes are found, the genesis of which is discussed.