Interictal positron computed tomography (PCT) with 18F-fluorodeoxyglucose was performed on 50 patients with partial seizures disorders. Electroencephalographic (EEG) monitoring was carried out during the metabolic studies using scalp and sphenoidal electrodes in 33 patients and stereotaxically implanted depth electrodes in 17. Four patients in this series had focal abnormalities on x-ray computed tomographic scans, but these were at the site of the presumed epileptogenic lesion in only 2. One or more discrete zones of hypometabolism were identified in 35 patients, and only 1 patient appeared to show focal interictal hypermetabolism. No quantitative relationship could be demonstrated between the degree of focal hypometabolism and either the frequency of interictal EEG spikes of the presence of focal nonepileptiform EEG changes. It was concluded that metabolic and electrophysiological techniques measure different aspects of cerebral dysfunction in seizure disorders. Although interictal PCT in patients with partial epilepsy usually demonstrates zones of hypometabolism this finding, per se, does not reveal the epileptic nature of the abnormality.