The purpose of this paper is to report five patients with chronic secretory diarrhea (maximum stool volume greater than 1 liter per day, duration 6 weeks to 8 years) in whom we could find no evidence of an endocrine tumor or of surreptitious laxative ingestion. All except one had severe hypokalemia. There was apparent improvement after treatment with prednisone in two patients and loperamide in one. The diarrhea resolved spontaneously in three patients and has undergone several temporary remissions in one patient. The last patient died after a severe unremitting illness. Extensive investigations failed to establish the etiology, but intestinal perfusion (carried out in four of the five patients) revealed secretion or abnormally low absorption of water and electrolytes in the jejunum and abnormally low absorption in the colon. The management of patients with chronic watery diarrhea is discussed.