The article reports on an infant which first in age of nine months and then again in age of 1.6 years had an episode of stupor. Laboratory investigation showed hyperammonemia and high values of transaminases. The differential diagnostic check up led to the diagnosis of citrullinemia in the age of 1.7 years by amino acid chromatography. The diagnosis could be confirmed by measuring enzyme activity in the liver. Therapy is protein-low feeding and supplementation of essential amino acids and arginine. A therapeutic trial with additional sodium benzoate did not show a positive effect. The patient made a significant step backwards in development during the second episode of stupor; however in the following months the retardation could be reduced markedly.
