In two patients with severe Parkinson's disease (PD) whose response to levodopa had decreased, the parkinsonian motor symptoms responded to acute and maintenance unilateral electroconvulsive therapy (ECT). Case 1 relapsed while taking antiparkinsonian medication 2 and 3 months after two brief courses of ECT. After another relapse, he received maintenance ECT and stayed well for 13 months. Case 2 relapsed 4 months after a course of ECT. Acute and maintenance ECT induced improvement for 14 months. Further relapses were treated with brief courses of ECT followed by maintenance ECT. Three and 4 years after their first ECT, the parkinsonian motor symptoms in these two patients are still markedly improved. Neuropsychological assessments did not suggest ECT-induced long-term cognitive impairment. We conclude that maintenance ECT should be considered in PD patients who relapse after having responded to an initial course of ECT. There is an urgent need for controlled studies.