In approaching the differential diagnosis of unexplained diarrheal disorders, separation of osmotic and secretory causes is important. The osmotic gap between measured stool osmolality and osmolality calculated from stool sodium and potassium concentrations is low in secretory diarrhea and high in osmotic diarrhea. Cholera, villous adenoma and bile salts are among the causes of secretory diarrhea. Causes of osmotic diarrhea include monosaccharidase deficiency, disaccharidase deficiency, excessive use of sugar-free gum and excessive ingestion of magnesium antacids.