BACKGROUND: Intraoperative alfentanil is known to increase the epileptic discharge in the adult seizure patients. This study hypothesized that alfentanil might localize an epileptogenic focus in pediatric seizure patients. METHODS: This study was performed in the pediatric seizure patients who undergo second-staged operation. Thirteen pediatric patients were enrolled and their epileptic foci were already suspected from first operation. After anesthetic induction, sevoflurane was maintained at 0.6% end-tidal concentration for study period. Electrocorticography (ECoG) was recorded for 5 minutes before and 5 minutes after alfentanil 20microgram/kg IV. During the ECoG recordings, the mean arterial pressure (MAP) and heart rate (HR) were continuously monitored. After the surgery, a pediatric neurologist analyzed the changes of spike frequencies of suspected ictal zone. The spike frequencies of suspected non-ictal zone were also calculated in five patients. The suspected ictal zone was defined as the most abundant spontaneous spiking area observed after first staged grid insertion. RESULTS: Alfentanil induced a significant increase in spike activity of suspected ictal zone in 12 out of 13 patients (median of 20 [ranged 10 to 100] vs 38 [ranged 20 to 100], P< 0.05). Alfentanil-induced increase of spike activity was prominent in the suspected ictal zone rather than non-ictal zone. There were no significant changes in the MAP and HR after administration of alfentanil. CONCLUSIONS: Alfentanil activates epileptiform activity of suspected ictal zone in pediatric patients with seizure disorder and can be used to assist in the localization of the epileptogenic focus during seizure surgery.