The effect of acute toluene exposure on behaviour and monoamine concentrations in the various brain regions were investigated in the rat. Toluene was adminstered via inhalation to rats at concentrations of 0, 1000, 10000, 40000 ppm for 20 min. During exposure to toluene, spontaneous locomotor activity was counted. After exposure, animals were sacrificed instantly and brains were separated. Regional concentratons of brain monoamines (norepinephrine, NE; dopamine, DA; 5- hydroxytryptamine, 5-HT) and its metabolites (3,4-dihydroxyphenylacetic acid, DOPAC; homovanillic acid, HVA; 5-hydroxyindole-3-acetic acid, 5-HIAA) were determined. The changes in locomotor activity during toluene exposure depended on the toluene concentration. At 1000 ppm concentration, spontaneous locomotor activity increased initially and thereafter decreased. At higher concentrations (10000 ppm and 40000 ppm), spontaneous locomotor activity decreased and eventually ceased. A regional analysis of VA, NE, 5-HT, VOPAC, HVA, and 5-HIAA indicated a significant decrease in VA concentrations in cerebellum and striatum while NE and 5-HT concentrations were significantly increased in the cerebellum and cortex. 5-HIAA concentrations were significantly increased in all brain regions. DOPAC concentrations were significantly increased in cerebellum and cortex while decreased in striatum. These results especially indicated that metabolic conversion of DA to HVA in striatum was highly increased by toluene inhalation. However, It remains to elucidate between behavioural responses and monoamine changes.