In a random-assignment trial to unilateral right and bilateral electrode placements, electroconvulsive therapy (ECT) stimulus intensity was titrated to just above seizure threshold for each of 52 depressed patients. Seizure threshold was quantified in units of charge. There was a 12-fold range in the minimum electrical intensity necessary to produce seizure. Sex, age, electrode placement, and the cumulative number of treatments were each associated with seizure threshold. Bilateral ECT had both a higher initial seizure threshold and a greater cumulative increase in seizure threshold compared with unilateral ECT. Clinical and research implications are discussed with respect to dosing strategies in ECT.