Abstract
A study of the fasting serum phenylalanine levels of 40 chronic schizophrenic patients and 15 normal controls was undertaken. The mean value obtained for the patients was 2.65 mg per cent; for the controls, 1.88 mg per cent. A t-test for the significance of the differences gave a p value of .003. Within the clinical subtypes of catatonic, hebephrenic, mixed, paranoid, and simple, only the mixed type did not show a significantly elevated level of phenylalanine. The significance of the results and the importance of the biochemical genetic approach to mental disorder are discussed.