Acidosis caused by intestinal bacterial d-lactate production occurs in ruminants engorged with carbohydrate. A similar phenomenon was identified in two children who developed recurrent episodes of metabolic acidosis and peculiar neurologic symptoms in response to increased dietary carbohydrate after major small bowel resections. Both children were found to have elevated plasma concentrations of d-lactic acid at the time of each episode. Acid base and neurologic abnormalities responded immediately to neomycin therapy. Among a number of microorganisms isolated from stool cultures of these patients, one anaerobic Lactobacillus acidophilus species produced large amounts of d-lactate in vitro. Reduction in carbohydrate intake in one patient tested led to a fall in d-lactate generation. We believe that excessive d-lactate production by intestinal bacteria, from malabsorbed carbohydrate, may produce metabolic acidosis and neurologic symptoms in children with small bowel resections.