39 adult patients with intractable epilepsy were successfully treated with high-dose monotherapy, using carbamazepine or phenytoin. In 27 patients seizures decreased 45% and in 19 of them decreased over 50% in 6 to 24 months of follow-up. The effect of reducing polytherapy to monotherapy was studied in 20 patients. In 19 of them this was possible without an increase in seizure frequency. In 10 cases seizure decreased over 50%. Individual dosage adjustment is preferably based on clinical judgment rather than on published therapeutic ranges. The causes of intractable epilepsy, individual dosage adjustment and seizure classification were discussed.