Tibolone has estrogenic, androgenic and progestational effects and is used in post menopausal women. It apparently has weaker effects on endometrial proliferation and mammary stimulation than conventional hormone replacement therapy. Aim: To compare the metabolic effects of tibolone (5 mg/day) and continuous combined conjugated estrogens/medroxyprogesterone acetate in postmenopausal women. Patients and Methods: postmenopausal women, aged 45 to 60 years old, receiving estradiol valerate and medroxyprogesterone were included in the study. After a two months wash out period, in a double blind fashion, they were randomly assigned to oral tibolone 5 mg/day or equine conjugated estrogens 0.625 mg + medroxiprogesterone acetate 2.5 mg/day (ECE/MPA). At baseline, 30 and 45 days of treatment, fasting serum osteocalcin, somatomedin C (IGF-1, insulin-like growth factor 1), growth hormone (GH), and follicle stimulating hormone and first morning urine calcium and creatinine were measured. Results: Thirty women were studied. There was more than 50% fall in urine calcium with either tibolone or ECE/MPA, while fasting GH or osteocalcin did not show significant changes. Serum IGF-1 increased significantly with tibolone at basal, 30 (+109%) and 45 days of treatment and did not change in the ECE/MPA group. Conclusions: Tibolone (5 mg/day) and ECE/MPA induced a similar reduction in urinary calcium. Tibolone increased serum IGF-1 levels. This may be due to undetected increment of overall GH secretion or to a specific action on IGF-1 generation from the liver and appears to be a novel differential effect of tibolone (Rev Méd Chile 2003; 131: 1151-56).