Hyperammonemia, which can cause brain damage, occurs in many different kinds of inborn errors of metabolism. The investigators propose to determine if short-term (3 day) treatment with N-carbamylglutamate can diminish hyperammonemia by enhancing ureagenesis in these patients. The investigators propose here a short-term (3 day) trial. If it succeeds, the investigators would consider more extensive long-term studies of the drug.