A group of 245 well nourished infants with acute diarrhea were screened for carbohydrate malabsorption by evaluating stool pH and reducing substances in the stools. Carbohydrate malabsorption was diagnosed in 28 cases (11%). Clinical features of carbohydrate intolerance were present in only one case. The duration of diarrhea after admission ranged from 1 to 13 days (mean 3.9 days). An oral lactose tolerance test was consistent with lactase deficiency in 32% of all cases. Thin layer chromatography showed many carbohydrates including monosaccharides in the stools, indicating that the defect in intestinal absorption was not specific for lactose.