In this study, the authors aimed to test the hypothesis that electroconvulsive therapy (ECT) may cause some alterations in hypothalamic-pituitary-thyroid (HPT) axis hormones and these responses may change throughout respective ECT sessions. Nineteen depressed inpatients (8 males, 11 females; mean age+/-S.D.: 44.77+/-10.59 years) considered suitable for ECT were included in the study. Each patient was exposed to 7 ECT sessions with general anaesthesia. The blood samples for measurements of thyroid-stimulating hormone (TSH), free thyroiodothyronine (fT3) and free thyroxine (fT4) were drawn before (baseline) and after propofol. immediately after ECT, and 30 and 60 min after ECT during the first and last (seventh) ECTs. In both the first and seventh ECTs, there was a significant increase in TSH levels 30 min after ECT compared to the pre-ECT values. Additionally, a significant decrease in post-ECT fT4 values compared to the baseline values was found only during the seventh ECT. No difference was detected in the TSH, fT3 and fT4 responses to ECT between males and females, and between bipolar and unipolar depressive patients. These results show that ECT may have sonic effects on the HPT system. However, whether there is a relationship between these neuroendocrine responses and the therapeutic effect of ECT is not clear. (C) 2002 Elsevier Science Inc. All rights reserved.