A double-blind, randomized, comparative study of the therapeutic efficacy and side effects of unilateral electroconvulsive therapy (ECT) given with two different stimulus types was carried out in the Kuffner Sanatorium, Horni Berkovice, Czech Republic. Brief or ultrabrief pulse stimuli were used in 48 hospitalized patients, ages 17-61 years, diagnosed with either schizophrenia (n = 42) or major depression (n = 6). All patients received eight unilateral treatments each. Their clinical state and presence of cognitive impairment were evaluated with a battery of tests and rating scales before ECT, after the last ECT, and 1 month later. Patients were markedly improved after the course of ECT, and the improvement was maintained 1 month later. There were no significant differences in the extent of improvement between the groups treated with brief- and ultrabrief-pulse stimuli. No deleterious effects on cognitive functions and memory were detected. In fact, there was a trend toward improvement in memory and other cognitive functions after ECT in both groups, with no significant difference between them. The two stimulus waveforms studied (brief and ultrabrief pulse) thus appear to be equally effective and free of deleterious effects on memory and cognition. The response in schizophrenic patients was remarkable and deserving of further study.