Collagenous colitis, reported four times until now, is characterised histologically by subepithelial tape-like collagen deposits in the rectum and colon. On endoscopy the mucosa appears normal or slightly oedematous. The main symptom is chronic watery diarrhoea without admixture of blood. The cause of diarrhoea is thought to be defective absorption of electrolytes in the colon as a consequence of the pathological collagen deposition. Using endoscopic, histological and electron microscopic findings two further cases of so-called collagenous colitis could be detected. In one of the two female patients chronic watery diarrhoea occurred connected time-wise with the administration of an H2 receptor antagonist. In addition, a clearly increased pancreatic polypeptide (PP) in serum was demonstrated without proof of an endocrinologically active (pancreatic) tumour.