Sprague-Dawley rats were treated with 10 µg/g b.w. thyroxine on days 8, 9 and 10 of life. This treatment had no effect on the development of the female diurnalpattern of plasma corticosterone or on the time of vaginal opening. Treated females cyclednormally and they showed compensatory hypertrophy (CH) of ovaries comparable tothat of vehicle-treated controls. Treated males responded to a combined ether-hemorrhagestress, as did controls, and they exhibited normal adrenal CH. Both treated males andfemales had lower body weights and reduced endocrine organ weights on day 49 of life