Patients 18 years of age or older with intractable epilepsy may be eligible for this study. Before entering protocol 00-N-0158, candidates will be screened under protocol 01-N-0139, Evaluation and Treatment of Patients with Epilepsy, with a medical history, physical and neurologic examination, chest X-ray, electrocardiogram, blood and urine tests, electroencephalographic (EEG) monitoring and magnetic resonance imaging (MRI) of the head.