Cow's milk protein sensitive enteropathy (CMPSE) is characterized by the following items: 1. The great majority of affected infants have not been breast fed or only for a few days. Additional risks are immaturity, preceding enteritis, trisomy 21, and abdominal operation in the newborn. 2. Half of the patients become ill during the first two weeks after starting cow's milk formula. The main symptoms are watery, mucus containing diarrhea, vomiting, abdominal distension, pallor and rapid weight loss. 3. In CMPSE the small intestinal mucosa shows varying degrees of inflammation and villous atrophy. Bloody stools refer to large bowel affection. 4. CMPSE is always transitory and usually persists for less than one year. Inadequate treatment leads to "severe protracted diarrhea" or "intractable diarrhea" syndrome. Soya-based formula should not be the diet of first choice, since secondary intolerance to soya proteins will frequently develop. Exclusive breast feeding during the first months of life is the best prophylaxis of CMPSE.