Schizophrenia is a chronic psychiatric illness. Disruption of the dopaminergic system has been suggested to be the pathogenic cause of this disease. The effect of Bifidobacterium longum BB536 (BB536) on schizophrenic behavior was investigated in an animal model. Daily administration of BB536 (10(9) CFU/mouse, p.o. for 2 weeks) was found to reduce rearing behavior augmented by the dopamine receptor agonist apomorphine and to decrease the resting level of plasma corticosterone and the ratio of kynurenine to tryptophan. These results suggest the potential of BB536 for supplemental treatment of the symptoms of schizophrenia.