A grossly mentally retarded infant was found to excrete large amounts of keto-acids; these were identified as the a-keto-acids corresponding to valine, leucine, and isoleucine. The free amino-acids were also found in great excess in the urine, blood, and CSF The urine had a characteristic smell resembling maple syrup; this seems to be largely due to the a-hydroxy-acids corresponding to valine, leucine, and isoleucine. It seems probable that this is an inborn error of the metabolism ofthe three amino-acids with a block at the oxidative decarboxylation stage. Tryptophan metabolism is also interfered with, as in phenylketonuria. Differentiation of this condition from phenylketonuria needs special care.

We thank Professor Alan Moncrieff for permission to study and report this case and for his interest in the work; the Research Committee of the Hospital for Sick Children for a Research Fellowship awarded to one of us (LIW); Professor Sir George Pickering for kindly providing laboratory facilities; Dr. G. Pampiglione for the EEG report; Dr. WW Payne for determining the fasting blood sugar; the nursing staff for their untiring co-operation; and Mrs. S. Phillips, Miss J. Wise, and Mr. P. Cousins for their expert technical assistance.