The sera of 59 patients with Crohn's disease (CD) and of 46 patients with ulcerative colitis (UC) were tested for autoantibodies (Aab) by indirect immunofluorescence with modern histochemical techniques using 19 different human tissues as antigenic substrates. Control collectives consisted of 19 patients with coeliac disease and of 100 healthy subjects. It was possible to demonstrate a specific marker for CD: Aab against exocrine pancreas (Pab) were present in 39% of the CD sera (UC 4%, coeliac disease 0%, healthy controls 3%). High Pab titres were only detectable in CD sera (29%). The CD-related autoantigen was demonstrated to be a component of normal pancreatic juice. Pab in CD were fundamentally different from those sometimes occurring in chronic and acute pancreatitis. It is suggested that CD is caused by autoimmune reactions against a component of pancreatic juice. Pab in CD correspond to Aab against intestinal goblet cells (Gab), which occurred exclusively in UC (28%). Pab and Gab, but obviously none of the other Aab investigated in this study, are of diagnostic value in chronic inflammatory bowel disease.