Three patients had exceptionally high seizure threshold, as determined by an empirical titration procedure. Initial seizure threshold was 896 mC in two of the patients. The third patient had an initial threshold of 336 mC that increased to 840 mC at the end of the course of electroconvulsive therapy (ECT), and remained elevated during a second course of ECT. All three patients were elderly men with complicated medical histories and ongoing low-dose benzodiazepine use. Each patient had an excellent response to ECT delivered with a custom modified device, capable of delivering more than twice the charge of ECT devices presently commercially available in the United States. Implications for the administration of ECT in patients with exceptionally high seizure threshold and the limitations of current device output are discussed.