Nonketotic hyperglycinemia (NKH) is an inborn error of amino acid metabolism caused by a defect in the glycine cleavage multienzyme complex resulting in high concentrations of glycine within the brain and spinal cord. Quantitative magnetic resonance spectroscopy ((1)H-MRS) allows measurement of absolute glycine concentrations within different parts of the brain in vivo. In addition, (1)H-MRS may be useful in monitoring treatment of NKH and to differentiate this disease from other disorders of glycine metabolism.