Findings are reported from a study of 20 patients receiving unilateral electroconvulsive treatment (ECT) on the right or the left side of the head. This study closely followed the design of an earlier investigation with the exception that evoked potential and direct current (DC) recordings, and neuropsychological testing were conducted a few hours after seizures instead of on the following day.Ictal and interictal electroencephalographic (EEG) findings confirmed observations made in the previous study. Again recording of evoked potentials in homologous areas on the right and left side of the head revealed no important differences between shocked and nonshocked hemispheres. The neuropsychological battery also failed to discriminate whether patients had received stimulation on the left or right side of the head.Clinically, as in the former series, outcome was similar for patients treated on the right or the left side of the head with minimal memory loss or confusion in either group. There was significantly more impairment of performance on one subtest of the Wechsler Memory Scale, a word association test, in patients treated on the dominant side of the head. This occurred after the fifth ECT and on termination of ECT but did not persist on follow-up retesting.Recording of slow potential activity was introduced in this study. There were highly significant differences in DC responses after five ECT's which mostly returned to pretreatment levels by the time of follow-up recordings.These findings were discussed in relation to the literature with suggestions for future scientific investigation.