There is evidence that brain norepinephrine may play a role in experimentally induced seizures in animals. Thus the present experiments were undertaken in an attempt to explore the role of brain norepinephrine in anticonvulsant activity of clonazepam. 6-Hydroxydopamine was given to newborn rats and PTZ-induced seizures were tested $70{sim}90$ days after birth and the rats were killed for determination of brain norepinephrine 8 days after the seizure test. Depletion of norepinephrine in the rat brain significantly potentiated the PTZ-induced convulsions and antagonized the effect of clonazepam on clonic seizures, tonic seizures and the number of seizures, but the latency to the seizure and the mortality has not been altered. However the 6-hydroxydopamine-induced antagonism of anticonvulsant action was surmountable by increasing the dose of clonazepam. These results show that brain norepinephrine may play an important role in seizure susceptability as well as in the anticonvulsant activity of clonazepam in rats.