The prognostic value of the TRH stimulation test was evaluated in 23 inpatients with major depressive disorder before and after a trial of ECT. In contrast to previous reports, the peak TSH response to TRH was significantly decreased after treatment compared with before treatment. This effect was consistent across individuals and subgroups (responders/nonresponders; unilateral/bilateral ECT). The particular ECT technique used in the study may account for the discrepancies between these findings and those previously reported by other authors.