The plasma levels of clobazam (CLB) and its main metabolite, N-desmethylclobazam (NDMC), were monitored in 46 epileptic patients receiving chronic CLB therapy in combination with other antiepileptic drugs (AEDs), including carbamazepine (CBZ), phenytoin (PH), phenobarbital (PB), and sodium valproate (VPA). A linear relationship was found between the plasma levels of CLB and NDMC, and between the doses and plasma concentrations of CLB and NDMC. The influence of AEDs on plasma levels of CLB and NDMC was investigated in 16 patients receiving 1 0 mg CLB daily. Results suggested that PH and PB, when taken with CBZ, significantly decreased the CLB plasma level, whereas VPA, when taken with CBZ, influenced plasma levels of both CLB and NDMC only slightly. The clinical efficacy of CLB was evaluated in 8 patients with complex partial seizures (CPSs). Five of the eight patients showed significant seizure reduction (>50%) for a short term (2-4 months) at the very beginning of the therapy. It was found that patients with CPSs without secondary generalization were more likely to respond to the drug than patients with secondary generalized CPSs.