Coixol (6-methoxybenzoxazolone) contained in Coix Lachryma-Jobi L. var. ma-yuen Stapf was compared with chlorzoxazone with respect to behavioral and EEG effects in mice and rats. Coixol 50-100 mg/kg, i.p. decreased locomotor activities of both species and produced hypothermia in rats. These effects of coixol were the same in potency as chlorzoxazone given in the same dose. Coixol was approximately twice as potent as chlorzoxazone in potentiating thiopental-induced sleep. This compound attenuated the writhing syndrome induced by 1% acetic acid and increased the threshold to jumping response induced by foot shock, to the same degree as seen with chlorzoxazone. Coixol was equipotent to chlorzoxazone in preventing convulsions induced by maximal electro-shock, while it was about 1.5 times more potent than chlorzoxazone in suppressing pentylenetetrazol-induced convulsion. Coixol 20-100 mg/kg inhibited the lever pressing response of hypothalamic self-stimulation in rats. In rats with chronically implanted electrodes, coixol 50-100 mg/kg induced drowsy patterns on the spontaneous EEG. The EEG arousal response to the external auditory stimulation was inhibited by the same doses of coixol, whereas it failed to suppress the arousal response to the midbrain reticular stimulation. These results indicate that coixol has pharmacological properties qualitatively similar to chlorzoxazone and acts as a central muscle relaxant with an anti-convulsant effect.