The behavioral responses of mice following intracerebroventricular (i.c.v.) injection of 9-methyl-7-bromoeudistomin D (MBED) were studied. Head-twitches were produced 20-90 min after the injection of 2, 20 and 200 nmol/mouse but such twitches were not significantly induced by caffeine (1000 nmol/mouse). The locomotor activity, as assessed by the Animex autometer, increased 0-120 min after the injection with doses of 2, 20 and 200 nmol/mouse, whereas a large dose of caffeine (500 nmol/mouse also increased the activity counts. Simultaneous injection of picrotoxin (3 mg/kg, s.c.) and MBED (50, 100 and 200 nmol/mouse) produced clonic and tonic extensive convulsions, but caffeine (1000 nmol/mouse) in combination with picrotoxin did not cause any type of convulsion.