Prolactin, cortisol, growth hormone and TSH serum levels (before and 15 minutes after treatment) were measured in 62 patients with endogenous depression randomly allocated to real or pseudo-ECT. Prolactin increased significantly more in those receiving real ECT than in those receiving pseudo-ECT, but the size of this effect had diminished by the time of the last (8th) treatment in the trial. Cortisol secretion was also significantly increased following the first treatment by real ECT, but this increase was of significantly smaller size in patients with delusions. Tolerance to the effects of ECT on cortisol secretion was not observed. No effects of ECT on growth hormone or TSH secretion were detected, and no clear evidence was obtained that endocrine responses can be used as a predictor of response to ECT.