Electroconvulsive therapy (ECT) is an appropriate clinical model to investigate blood flow during seizures. In this study cerebral blood flow velocity (CBFV) was measured during 40 ECTs in 10 patients by means of transcranial Doppler sonography. EEG was recorded continuously. Under general anesthesia, the pre-convulsive blood flow velocity (Vmean) decreased significantly. After ECT, we measured a dramatic increase in Vmean which was significantly greater in the left MCA than in the right MCA. After termination of seizures, flow velocities returned to baseline levels. The striking increase in cerebral blood flow velocity reflects excessive cerebral metabolism during convulsive neuronal activation. The left hemisphere seems to be more sensitive to electrical stimuli as was indicated by its predominant augmentation of CBFVs.