BACKGROUND: Elecroconvulsive therapy (ECT) is frequently associated with cardiovascular complications such as hypertension and tachycardia. The aim of this study was to evaluate whether clonidine given as an oral preanesthetic medication would influence the hemodynamic stress response, peripheral oxygen saturation and seizure duration which follows ECT. METHODS: Twenty-two ASA physical status I, II patients with major depressive disorders were included in a crossover study design and assigned randomly to either a control group who received placebo, or a clonidine group who received oral clonidine of 3 microgram/kg 90 min before preparation of ECT. All patients received glycopyrrolate 0.2 mg intramuscularly 60 min before anesthetic induction. Electrocardiography, pulse oximetry, and blood pressure monitors were applied to all patients. Patients were pre-oxygenated with 100% O2. Patients received thiopental 2.5 mg/kg and succinylcholine 0.5 mg/kg for anesthetic induction. Noninvasive mean arterial blood pressure (MAP), heart rate, and oxygen saturation were recorded just before test drug administration, immediately before ECT, and each minute for five minutes after ECT. The times from ECT stimulus to the cessation of clonic-tonic motor activity in the "isolated" arm were noted. RESULTS: There was a significant decrease in MAP (P = 0.007) through the peri-ECT period in groups with oral clonidine pretreatment (3 microgram/kg) relative to the control group. There were no significant differences in heart rate and peripheral oxygen saturation values between two groups. The duration of motor seizure activity was similar between the clonidine pretreatment and placebo groups. CONCLUSIONS: We conclude that oral clonidine 3 microgram/kg as a pretreatment medication is effective in attenuating the MAP increase in routine ECT.