AbstractObjectives: Even low concentrations of organic solvents may cause acute effects on the human central nervous system. The German MAK (threshold limit value) of methanol is 200ppm. The aim of this study was to investigate whether acute exposure to 200ppm methanol causes adverse effects, measured by EEG, and moreover, whether it is possible to differentiate between sedative and excitatory effects with this method. Methods: Twelve healthy subjects were exposed for 4h to 200ppm and to 20ppm (control) in an exposure chamber in a cross-over design. The EEG was recorded before (reference) and at the end of each exposure with, the subjects eyes closed and opened and during a choice reaction test (color word stress test). Spectral power was calculated by fast Fourier transformation. Subjective symptoms and effects of blinding with 20ppm methanol were assessed by questionnaires. Results: The study was a single-blind one. During subjects exposure to 200ppm, their scores for prenarcotic and irritating symptoms were not different from controls. In the closed-eye condition of subjects, the spectral power of the -band and of some electrodes of the -band was significantly less at the end of exposure to 200ppm, than that of controls. In the open-eye condition and during the color word stress test no significant changes were found. Conclusion: The changes in the -band suggest a slight excitatory effect of 200ppm methanol. The effect was weak, as scores of acute symptoms did not change. With respect to our results, it is not necessary for the MAK value to be decreased.