The Clinical Epilepsy Section has been studying the clinical pharmacology of old and new antiepileptic drugs. In spite of the fact that many such medications have been marketed for many years, there is still a great deal to be learned about the proper use of the drugs which are already in our armamentarium. Advances in pharmacology in the past 20 years have allowed the use of new approaches and techniques to gain insight into the proper use of our currently available drugs. In addition, the Clinical Epilepsy Section is involved in clinical trials of new antiepileptic drugs, such as sodium valproate which was recently marketed in the United States. The pharmacologic evaluation of these drugs is coupled with efficacy studies which are carried out by intensive monitoring techniques including videotape analysis of epileptic seizures with simultaneous electroencephalographic recording and long-term telemetered EEG recording. The daily determination of antiepileptic drug levels is an integral part of the on-going studies. Recent emphasis has been on the efficacy of single drug therapy in patients with complex partial seizures, and on mechanisms for valproic acid-phenobarbital interaction.