This article critically reviews the six controlled studies of the antidepressant effects of right unilateral versus left unilateral ECT (R-ECT, L-ECT), contrasting them with results recently obtained in double-blind, random assignment comparison of the two methods, using a square-wave stimulus, widely spaced temporoparietal electrode placement, and markedly supra-threshold stimulus charge. The author challenges the prevalent belief in a therapeutic advantage of R-ECT versus L-ECT, proposing instead the contrary case for a therapeutic advantage of L-ECT, based on the interaction of a hypothesized interhemispheric seizure threshold difference and a maximally efficient method of stimulus delivery.