1. Current guidelines on the practice of Electroconvulsive Therapy (ECT) suggest that antidepressant medications should be discontinued prior to the course of therapy. However, the practice of withholding potentially helpful medication is debatable because the effects of these medications on seizure duration remain unclear. In particular, there is a lack of empirical knowledge about the effects of Selective Serotonin Reuptake Inhibitors (SSRIs) on ECT treatment. 2. Therefore, we investigated and compared the effects of SSRIs and tricyclic antidepressants (TCAs) on seizure duration after the first bilateral ECT treatment. 3. The diagnosis of major depressive disorder was made using the DSM-IV criteria. Both patient groups were age- and sex-matched. ECT was indicated for acute suicidal acts or refractoriness to medications. All patients had received antidepressant treatment for at least eight weeks and were receiving at least the recommended dose of medication. All patients were ECT treatment-naïve and we measured the seizure duration after the first bilateral ECT treatment. 4. There was no significant difference between electrical charge applied to either group. Between the TCA and SSRI group the seizure duration was not significantly different: 33.2 seconds and 31.4 seconds respectively.