The effect of centrally (0.3-30 ng/kg) and peripherally (0.01 μg/kg-1.0 mg/kg) administered clonidine on PTZ-induced seizures was studied in rats. At low doses, dose-dependent decreases in the duration of seizures was observed but at higher doses the duration returned to control levels. Anticonvulsant activity was antagonized by yohimbine (100 μg/kg i.p.) indicating α2-adrenoceptor involvement, whereas the second phase of the response was antagonized by prazosin (10 ng/kg i.c.v.) indicating that it involved α1-adrenoceptors.