This study examines the relationship of serum prolactin changes (delta PRL) to variations in electrode placement after controlling for differences in the convulsive threshold. Previous studies showing greater release of PRL with bilateral (BL) compared with right unilateral (RUL) electrode placement were conducted without knowledge of the convulsive threshold. Twenty-two patients each received threshold RUL, threshold BL, 2.25 times threshold RUL, and 2.25 times threshold BL ECT. Serum PRL was collected 5 min before and 15 min after each electroconvulsive therapy (ECT). The convulsive threshold was greater for BL than RUL electrode placement. delta PRL was greater with BL than RUL ECT at comparable relative stimulus intensities. delta PRL was not correlated with seizure duration or absolute stimulus dose.