PURPOSE: To evaluate MRI and histopathologic findings of toluene inhalation rat brain. MATERIALS AND METHODS: Forty-eight Sprague-Dawley rats, weighing 200-300g, were divided into six groups : the control group and five experimental groups each of eight rats, divided as follows, according to the concentration and duration of inhalation of toluene : 2500 ppm of toluence vapor for 2 hours only, 2 hours daily for 1 week, and 2 hours daily for 3 weeks ; 4000 ppm of toluence vapor for 2 hours only and 2 hours daily for 1 week. For all these five groups, a 0.02 m3; whole body exposure chamber was used. Spin echo and field echo (FE, gradient echo) MR images were obtained at 0.5 T, and then histopathologic examination of the brain was performed. MR signal changes were statistically assessed for contrast to noise ratio (CNR). RESULTS: On T2-weighted MR images, the toluene-inhalation groups revealed diffuse hypointensity in the corpus striatum and thalamus, and diffuse hyperintensity in cerebral white matter, with statistically significant CNR change, compared with the control group. On T1-weighted and FE images, CNR differences in the corpus striatum, thalamus and cerebral white matter between the toluene inhalation groups were not statistically significant. Histopathologic study of these groups showed (1)neuronal degeneration such as shrinkage of neuronal cells and increase of the number of autophagosomes, (2)myelin degeneration and regeneration, and (3)focal axonal degeneration, In groups in which toluene inhalation was at higher concentrations and for longer, these phenomena were more extensive. CONCLUSION: As seen on MRI, toluene inhalation changes the signal intensity of the corpus striatum, the thalamus, and cerebral white matter. Neuronal, myelinic and axonal degeneration probably contribute to these signal changes.