The difference on various enzymic activities and excretion of urinary metabolites of tryptophan in the rat, mouse, guinea pig and rabbit were observed quantitatively. Level of liver tryptophan oxygenase induction by L-tryptophan and cortisone were showed so highly activity at rat and mouse than guinea pig and rabbit. Then the enzyme of rat and mouse existed both apo-and holo-type in the liver, but that of guinea pig and rabbit was holo-type alone. Furthermore, the activity of kynurenine-3-hydroxylase, kynurenine transaminase and kynureninase in the liver has been found to differ considerably by four species, and kynurenine-3-hydroxylase activity of rabbit was in particular low. The pattern of urinary metabolites of tryptophan by ppc was so similar between rat and guinea pig, but that of rabbit and mouse was distinct from other species. On the excretion of kynurenine, anthr-anilic acid, kynurenic acid and xanthurenic acid, three metabolites except xanthurenic acid in the urine of rabbit were recongnized so much than other animals
