Cow milk protein intolerance (CMPI) is an allergic process affecting the distal gastrointestinal tract in infants. As such, it often presents as diarrhea without or without the presence of gross rectal bleeding in infants ranging in age from birth to 6 months of age. Children display symptoms of abdominal disress including cramping, colic, or feeding difficulties. Emesis after feeds may also be present. Affected children display loose and more frequent bowel movements. Stools in these patients may contain mucus as well as microscopic or visible blood. In most patients, the diagnosis is based on an appropriate clinical history and supporting physical exam (typically normal). Treatment involves removal of the offending dietary antigens which include cow or soy milk protein. A small percentage of patients (< 5%) require formal endoscopic study. The mucosa in these patients appears erythematous, friable, and can display a patchy distribution of inflammation. Histologic exam reveals varying degrees of eosinophic infiltration of the intestinal tissue. Eosinophilic crypt abscesses, or collections of eosinophils within the intestine can also be seen. Patients responding to therapy will display normalization of stool frequency, decreased symptoms of abdominal discomfort, and an absence of gross or microscopic intestinal bleeding.