The concentrations of monoamines and their metabolites (refer to Tables 1 and 2 about each material) in the rat whole brain except for the olfactory bulb and the pituitary gland were measured after the administration of lithium (Li), carbamazepine (CBZ) and valproic acid (VPA) for 14 days. The plasma levels of three drugs were each 0.96 +/- 0.21 mEq/L (Li), 14.216 +/- 3.78 micrograms/ml (CBZ) and 53.341 +/- 31.76 micrograms/ml (VPA). The brain concentrations of monoamines and their metabolites are shown on Tables 1 and 2, and their change rates of the administrated groups to the intact group as control on Figs. 1 and 2. Some changes were similar, i.e. tryptophan, 5-HT, 5-HIAA and L-DOPA seemed to increase, and normetanephrine and 3-MT seemed to decrease in common in three groups. On the contrary, tyrosine, 3-o-methyldopa, DOPAC and HVA increased significantly in only VPA group. It is an uncertain supposition that the common increases or decreases on this study may show the common mechanism among three mood stabilizers, but these changes are very interesting because many reports have mentioned the relation between mood disorder and monoamine neurotransmission. Especially, the common increases of tryptophan, 5-HT and 5-HIAA and the common decreases of 3-MT and normetanephrine may suggest some relation to the pharmacological mechanism of the mood stabilizer.