Different doses of melatonin (50-100 mg/kg i.p.) were tested for their ability to suppress complex partial seizures in the amygdala kindling model of the rat. Thirty minutes after injection of 75 or 100 mg/kg melatonin, the current threshold necessary to elicit epileptic afterdischarges (ADT) was significantly increased by about 200 or 250%, respectively. These doses were also sufficient to suppress generalised seizures at threshold current. All doses of melatonin decreased body temperature by more than 0.5 degrees C, but caused no pronounced ataxia. Seizure susceptibility in terms of ADT changed with the time of the day but seems not to depend on the circadian variation of endogenous melatonin, since the highest ADT was found in the morning when endogenous melatonin levels are low.