Studied the effects of injections of parachlorophenylalanine and phenylalanine, and the ingestion of diets varying in phenylalanine and tyrosine content for their effects on susceptibility to audiogenic seizures. using 571 hybrid mice. All of these treatments increased seizure susceptibility. When these phenylketogenic treatments were paired with injection of ALPHA-methyl tyrosine, further increases in seizure susceptibility were observed. The effects of injections of parachlorophenylalanine and phenylalanine on levels of serotonin and norepinephreine in brain were investigated; these treatments lowered levels of serotonin in brain without affecting levels of norepinephrine. The possible role of these amines in determining seizures susceptibility is discussed. (26 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1969 American Psychological Association.