Rats were exposed to trichloroethylene (TriCE) and tetrachloroethylene (TetraCE) at concentrations of 200, 400, and 800 ppm for one month. The effects of inhalation exposure on neurotransmitter candidates of the rat brain were studied. Changes in the acetylcholine (ACh) content of the striatum were investigated by pyrolysis gas chromatography. The dopamine (DA) in the striatum, norepinephrine (NE) in the hypothalamus, NE and serotonin (5TH) in brain regions containing cortex and hippocampus were analyzed by high-performance liquid chromatography. (1) The DA in the striatum was slightly increased by TriCE and decreased by TetraCE, but the change were not statistically significant. (2) The ACh in the striatum was markedly reduced dose-dependently by these two organic solvents. The decreases in ACh at 800 ppm of TriCE and TetraCE were significant (p<0.05). (3) The NE was slightly increased by these solvents, except that the NE in the cortex and hippocampus was reduced by TriCE. (4) The 5HT in the cortex and hippocampus was increased by TriCE and TetraCE, but the increase was not statistically signi-ficant. It is suggested that long-term exposure to organic solvents may cause some disturbance of the cholinergic neurons of the central nervous system.