Acute electroconvulsive therapy has anticonvulsive effects. The aim of the present study was to investigate the anticonvulsive efficiency of maintenance electroconvulsive therapy. Records of patients treated with maintenance electroconvulsive therapy were screened retrospectively, and the changes in seizure duration were measured. The patients were subdivided into responders and non-responders. Responders had no significant seizure duration changes within the first week of maintenance electroconvulsive therapy. In contrast, the seizure duration of the non-responder group increased significantly within the first week. It was concluded that the early increase in seizure duration at constant energy could be predictive of relapse.