We studied the role of the noradrenergic system in the seizures of epileptic El mice. To this end, the anticonvulsant activity of adrenergic drugs was tested with a scoring method, and the binding of [3H]dihydroalprenolol, [3H]prazosin and [3H]yohimbine was evaluated in whole brains and various brain regions from stimulated and unstimulated El mice, and their maternal ddy mice. The seizures of El mice were inhibited by noradrenaline, phenylephrine, oxymetazoline, clonidine and yohimbine in a dose-dependent manner. These preventive effects of alpha-adrenoceptor agonists were antagonized by pretreatment with alpha-adrenoceptor antagonists. The preventive effect of yohimbine was reversed by pretreatment with clonidine or alpha-methyl-p-tyrosine, although the latter drug did not affect the anticonvulsant effect of clonidine. The binding of [3H]dihydroalprenolol was the same in the three groups of mice. More [3H]prazosin was bound in the cerebellum and striatum, and there were more [3H]yohimbine binding sites in the whole brain, cerebral cortex, hippocampus and brainstem of stimulated and unstimulated El mice than in the same areas of ddy mice. These findings suggest that up-regulated alpha 1- and alpha 2-adrenoceptors are involved in the inhibition of the seizures of El mice.