Investigated the effects of unilateral left (UL), unilateral right (UR), and bilateral (B) ECT on the performance of right-handed male patients on the Wechsler Memory Scale and two tests of the Williams battery, which provided eight independent measures of verbal memory and two of visual-spatial memory. Patients were tested three times: (1) within 1 week prior to ECT; (2) within 30 minutes after the sixth ECT; (3) 10 days after the sixty ECT. Double blind procedures were maintained carefully. Results showed a significant loss on second testing followed by a significant improvement 10 days later for all ECT groups compared with matched controls. There was some tendency for the UR group to show the least impairment on verbal measures and the UL group to show the least impairment on visual-spatial memory test of the WMS, but most of the differences between UL and UR groups and between each of these and the B group were not significant. The most sensitive test in differentiating among the ECT groups was the brief Verbal Learning subtest of the Williams battery.