In recent years, electrophoretical studies of proteins in gastrointestinal juices have attracted increasing interest. Saliva was studied, mainly in relation to dental problems 1--7 ; gastric juice in relation to the intrinsic factors-lo or physiological and pathological problems ]2-21; bileZ4p 25, especially in relation to bile stone formation 22y 23 and the pancreatic juice of animals 2~~0 for its protein composition and enzyme distribution. Separation of the fractions by means of paper electrophoresis was described in the papers 1, 2, 9,12, 13, 15, li--20, 22--26, 29, 30. Technical difficulties proved to be of major importance, therefore, the results of many investigations were incomparable, or contradictory as far as numbers, significance and the quantitative ratio of the protein fractions were concerned. Thus it is hardly possible as yet to describe the “normal pictures”. With few exceptions (e.g. 21), changes under pathological conditions have received little attention. Comparative studies on human material are practically lacking. This paper deals with the results of more than 5000 paper electrophoresis diagrams of human gastrointestinal juices. We tried to find the optimal conditions for the separation of the fractions. A number of detection methods were developed and compared with various existing techniques. The discussion of the results will be restricted mainly to the qualitative aspects of the diagrams.