Analysis of the free amino acid pool in the chestnut fruit (Castanea sativa) shows that it is high in y aminobutyric acid. A metabolic connection between arginine and y-aminobutyric acid is evident. Three enzymatic activities are involved: L-arginine ureohydrolase, L-ornithine 2-oxo-acid aminotransferase and L-glutamate carboxylyase.