Patients between 5 and 65 years of age who have had epilepsy for two or more years and have had at least one seizure a week for at least 6 months may be eligible for this 18-week study. Their seizures must come from a neocortical focus-that is, near the surface of the brain. Candidates will be selected from the NIH Epilepsy clinic and will be screened with an electroencephalogram (EEG), magnetic resonance imaging (MRI) scans, and blood tests.