[en] Objective: To investigate the clinical significance of determination of changes of serum thyroid hormones levels after operation in patients with pituitary ademoma. Methods: Serum FT₃, FT₄,TSH (with CMA) and rT₃ (with RIA) levels were determined in 50 patients with pituitary adenoma both before and one week after operation as well as in 86 controls. Results: The serum FT₄ and rT₃ levels in the patients before operation were significantly lower than those in controls, but the FT3 and TSH levels were not significantly different. Post-operatively, FT3 levels dropped markedly, but rT₃ levels rose markedly while the FT₄, TSH levels were not greatly changed. Conclusion: There were mild thyroid dysfunction in patients with apparently nonfunctioning pituitary adenoma. (authors)