A family is described in which the 3 children presented with episodes of severe metabolic acidosis secondary to minor infections. 2 of them died, and 1 of these was severely retarded. The sole surviving child is 6 years old and is normal with respect to physical and mental development. Gas chromatography of the urine obtained during episodes of ketoacidosis showed the keto and hydroxy acids characteristic of maple syrup urine disease, and thin layer chromatography of the plasma and urine showed greatly increased concentrations of the branched chain amino acids. The urine and plasma of the surviving child was chromatographically normal between episodes. The leucocyte branched chain keto acid decarboxylase activity in this patient and her father was reduced. The range of features in this family with intermittent maple syrup urine disease illustrates the necessity for prompt and careful investigation of metabolic acidosis of unknown aetiology.