Fifteen infants developed pneumatosis intestinalis (PI) during an episode of severe diarrhea. They presented radiolucent streaks within the wall of the intestine. A marked deficit of sodium and potassium ions was confirmed by intracellular concentrations and a balance study. Carbohydrate tolerance was diminished in all infants; seven had lactose intolerance during the episode of diarrhea prior to the development of PI. Following the acute stage, three patients tolerated glucose but not disaccharides, and seven with bacterial growth in duodenal cultures were intolerant to all carbohydrates. Upon carbohydrate elimination, diarrhea improved and PI was resolved. A gradual recovery in monosaccharides, disaccharides, and finally lactose tolerance occurred within four months. Pneumatosis intestinalis complicating diarrheal disease of infancy may result from gas accumulation from bacterial fermentation in malnourished potassium deficient individuals.