123I-Iomazenil SPECT was performed in 17 patients who were considered candidates for surgery of epilepsy because of medically intractable complex partial seizures. In addition to this examination their presurgical evaluation consisted of long term ictal EEG-CCTV monitoring, CT, MRI and 18FDG PET. In eight patients intracranial ictal EEG recordings were performed. SPECT was assessed visually while PET data were analyzed quantitatively. Both SPECT and PET were compared to ictal EEG data and showed asymmetries in over 80% of patients in agreement with EEG findings. These three methods were in agreement in 65% of patients. SPECT showed abnormality contralateral to the EEG focus in one patient (6%) while PET always demonstrated ipsilateral dysfunction. It is concluded that 123I-Iomazenil SPECT may be considered a more economical and more widely available alternative to 18FDG PET in the presurgical evaluation of patients with medically intractable complex partial seizures. In this respect 123I-Iomazenil specifically reflects functional changes in the membranes of neurons while 18FDG is related to glucose metabolism not only of neurons but also of glial cells.