Thirty-one epileptic patients with seizures refractory to conventional anticonvulsants were treated by adding clorazepate dipotassium to their regimen. Twelve cases showed improvement in seizure frequency, three of whom attained a seizure free state. Response to clorazepate was not related to the type of epilepsy, but patients with secondary generalized epilepsy tended to be less responsive than those with partial epilepsy. Among the various seizure types, generalized tonic-clonic seizures and simple partial seizures showed, although not significant, a tendency to be more responsive to clorazepate therapy than other seizure types, including complex partial seizures, atypical absence, atonic seizures, and tonic seizures. Drowsiness was the main adverse effect, of which 14 patients complained. Six patients were withdrawn from clorazepate because of drowsiness, but in the remaining 8 patients, this side effect disappeared within a week. The appearance of adverse effect was not related to the dose of clorazepate given. Clorazepate may be an effective secondary anticonvulsant in the treatment of intractable epilepsy.