Abstract
Phenylpyruvic acid was demonstrated in the blood of 39 patients affected with phenylpyruvic oligophrenia. The values ranged from 0.31 to 1.78 mg. per 100 ml. of plasma. A significant increase of phenylketonemia was observed following ingestion of DL-phenylalanine, the D-form causing considerably greater increase than the L-isomer. Feeding of phenylpyruvic acid resulted in a sharp increase of phenylketonemia. The significance of these findings is briefly discussed.