Caffeine lengthens ECT seizures, perhaps by lowering the convulsive threshold. The authors assessed the impact of caffeine on the convulsive threshold and seizure duration. The convulsive threshold and seizure durations of 12 inpatients receiving right unilateral ECT were determined with and without caffeine pretreatment. Caffeine did not change the convulsive threshold, but it did lengthen seizure duration. Caffeine's lengthening of seizure duration without affecting the convulsive threshold is an uncertain benefit in right unilateral ECT.