The contents of tyrosine (Tyr), tryptophan (Trp) and their metabolites in brain regions of ddY, non-stimulated E1 (E1 (-)) and stimulated E1 (E1 (+)) mice were measured using a Three Dimensional HPLC System. In the cerebral cortex, striatum, midbrain and cerebellum, Trp contents of E1 (+) mice were higher than those of ddY and E1 (-) mice. The contents of 5-hydroxytryptophan in E1 (-) or (+) mice brain were lower than those in ddY mice except in the medulla oblongata. Those in the cerebral cortex, and midbrain of E1 (+) mice were lowest. Brain regional serotonin (5-HT) contents of E1 (+) mice seemed to be slightly higher than those of ddY and E1 (-) mice. In the cerebral cortex, hippocampus, medulla oblongata and cerebellum of E1 (+) or (-) mice, the kynurenin contents were remarkably high compared to ddY mice. Although brain Tyr content did not differ between the three groups, the dopamine contents in the cerebral cortex, hypothalamus and striatum of E1 (+) mice were lower than those in ddY mice, and those in the cerebral cortex and striatum of E1 (+) mice were higher than those in E1 (-) mice. The norepinephrine contents did not differ between E1 (-) and ddY mice, but some brain regions of E1 (+) mice had higher levels. The content of 3-methoxy-4-hydroxyphenylglycol of E1 (-) mice was lower, and in E1 (+) mice was lowest in 7 brain regions. The tyramine contents in E1 (-) or (+) mice brains were higher than those in ddY mice, except in the midbrain of E1 (+) mice. These data, suggest a possible genetic metabolic abnormality of Try and Tyr in the brains of E1 mice.