• Patients with nonketotic hyperglycinemia generally have intractable seizures that are poorly responsive to anticonvulsant medication. No effective treatment has been consistently reported. In three patients with nonketotic hyperglycinemia, the oral administration of sodium benzoate in dosages designed to lower the cerebrospinal fluid concentration of glycine was followed by an abrupt change from frequent major seizures before treatment to no seizures, or only occasional minor ones, after treatment. This attenuation of seizures was associated with a decrease in the concentrations of glycine in both plasma and cerebrospinal fluid. There was no evident change in psychomotor development.