More than 20 instances of maple syrup urine disease (MSUD) have been described since 1954. Most were infants, who manifested in the first month of life a maple syrup odor in their urine and a clinical pattern of fits, episodic rigidity, lethargy, and poor suck. When measured, their blood and urine levels were found to be elevated for the branched-chain amino acids (valine, leucine, and isoleucine) and the α-keto-acids derived from them. Our purpose is to record the family pedigree of another infant with MSUD and to report some clinical and biochemical correlations observed during the management of the infant. Family Pedigree In 1959, Lane reported on an infant (X in Fig 1) seen in this hospital with MSUD. She mentioned that a sister and a cousin of her patient had died at ten days of age with clinical findings which were highly suggestive of that disease.1 Subsequent family