Schedule of administration (number of ECT per week and total number of treatments in the course) is one of a number of factors that may significantly influence the degree of cognitive impairment induced by ECT. We examined the effect of twice (ECT x 2) versus three times weekly (ECT x 3) bilateral ECT on cognitive function, particularly memory, in patients with major depression. Two studies were conducted, both double blind and controlled by the administration of simulated ECT (anesthesia and muscle relaxant only with no electrical stimulation). The results of these studies showed that the antidepressant effect of the two schedules, when assessed at the end of the ECT course, was equal. Speed of response was significantly greater with ECT x 3 but this schedule induced more severe memory impairment, even when the number of ECT in the series was not significantly different between the two groups. These findings are in general accordance with other studies that were similar in design although not as rigorously controlled. They support the conclusion that ECT x 2 is the more appropriate schedule for regular clinical practice unless speed of response is an overriding concern. In an era when patients administered ECT tend to be older and are more likely to manifest cognitive impairment for other reasons, choice of schedule is of particular relevance along with other factors such as electrode placement and stimulus intensity that influence ECT-induced cognitive impairment.