&NA;Morphologic and functional changes of the intestinal mucosa have been widely observed following abdominal radiation. We report the case of a patient who had recurrent subacute intestinal obstruction, weight loss, and malnutrition following intensive radiation therapy for peritoneal carcinomatosis. Her symptoms resolved, and her nutritional status improved and was maintained for more than eight months with the exclusive use of an elemental diet: Mead‐Johnson 3200 AS made of 10 g/100 g casein hydrolysate, 14 g/100 g triglycerides (18 per cent of which were M.C.T.), and 67 g/100 g carbohydrates. A conventional low‐residue diet was not tolerated. A control diet similar to 3200 AS, but with whole casein replacing casein hydrolysate and L.C.T. replacing the 18 per cent M.C.T., resulted in mild diarrhea, nausea, and an eight‐fold increase of fecal fat. Possible roles of M.C.T., L.C.T., and protein hydrolysate are discussed.