THE CATABOLIC deamination and transamination of protein results in the formation of ammonia, a noxious substance that must be detoxified and excreted. Retention of ammonia in adults is usually due to advanced liver disease or portocaval shunts and is often associated with encephalopathy. In contrast, ammonia retention in children is usually due to an inherited metabolic defect of the urea cycle. This article describes an abnormality of urea metabolism, presumably due to a deficiency of carbamyl phosphate synthetase. Although the principal clinical manifestations were those of ammonia intoxication, hyperglycinemia and a persistent acidosis, with intermittent ketosis, and hyperlipemia were also noted. Report of a Case This 5-week-old girl was transferred to Babies Hospital because of unexplained vomiting and intermittent coma. She was the result of the sixth pregnancy of unrelated parents. The first two pregnancies ended in miscarriages, the third in an ectopic pregnancy. The fourth, a girl, died