A girl aged 3 years and 11 months, with recurrent episodes of unexplained metabolic acidosis, hepatomegaly, and fasting hypoglycemia unresponsive to glucagon, showed profound falls in blood glucose levels in response to oral fructose and glycerol challenge. In vitro analysis of her hepatic glycolytic and gluconeogenic enzymes demonstrated absent fructose-1,6-diphosphatase activity. A therapeutic trial of orally given folic acid, 30 mg daily, did not improve her tolerance for fructose and glycerol. Over the next two years she showed improvement in tolerance to fasting, and to fructose and glycerol loading on dietary management.