Although electroconvulsive therapy (ECT) has been employed for treating depression for more than 60 years, its mechanisms of action are yet unknown. To clarify the ECT effects on brain function, we examined cerebral blood flow (CBF) using single photon emission computed tomography at 3 time points-few days before an ECT course (Pre) and approximately 5 days (Post 1) and 1 month (Post 2) after the last ECT session. Eight depressive patients completed the study. In all the patients, the depressive symptoms improved after the ECT course, and major cognitive impairment was not observed at any time point. At Pre, the regional CBF (rCBF) in the widespread areas in the frontal lobe and limbic regions including cingulate cortex and parahippocampal gyrus was lower in the patients than in the normal controls. At Post 1 and Post 2, the rCBF in the frontal and limbic regions continued to be lower in the patients than in the controls although the successive recovery of decreased rCBF in the frontal region was observed. Regarding the time course among the patients, the rCBF in the right medial frontal region significantly increased (toward normal) at Post 2, not at Post 1. These findings suggest that depressive patients have decreased CBF in the frontal and limbic regions, and the medial frontal region plays a crucial role in ECT and recovery from depression. Further, patients who have undergone ECT treatment for depression should be carefully observed because brain functions continue to change even after a successful ECT course.