Objective: To study whether hormone replacement therapy (HRT) or Tibolone has an effect on pulmonary function in postmenopausal women. Methods: Seventy-five postmenopausal women without any risk factor for pulmonary disease were included in this randomized, prospective study. Fifty women had undergone natural menopause and 25 had had a hysterectomy/ooforectomy. Twenty-five natural menopause women were randomly allocated to two groups: 25 patients (Group I) were treated with Tibolone 2.5 mg/day, 25 patients (group II) with Estradiol Hemihidrate 2 mg+ Norethindron Asetate 1 mg/day. Twenty-five induced menopause women were treated with 17beta-estradiol 2 mg/day. Lung function tests including forced vital capacity (FVC), forced expiratory volume (FEV1), FEV1/FVC, forced expiratory flow rate over the 25-75% of the forced vital capacity volume (FEF25-75%), and peak expiratory flow rate (PEF) were evaluated at the beginning and 3 months after the treatment to assess the effects of HRT and Tibolone on respiratory function. Results: Regardless of HRT types a significant difference was observed in FVC and FEV1 after 3 months of the therapy (P = 0.001, 0.0001, respectively). No significant difference was found between pre and post therapy values in the other parameters (P > 0.05). Conclusions: We determined a significant increase in FVC and FEV1 parameters of pulmonary functions after 3 months of the therapy regardless of HRT types. Therefore, we think that HRT regimens have modifying effects on pulmonary function in postmenopausal women. (C) 2003 Elsevier Ireland Ltd. All rights reserved.