The effects of 6 months of hormone replacement therapy by transdermal estradiol patches (0.05 mg/day for 21 days) and oral progestogens (10 mg/day for 10 days) on hypothalamic-pituitary-ovarian function was evaluated in 32 perimenopausal women, aged 42-47 years, with irregular anovulatory cycles and menopausal symptoms. Hormone levels evaluated on the 8th and 24th day of the cycle preceding therapy showed follicle-stimulating hormone (FSH) levels above 15 mIU/ml, estradiol less than 45 pg/ml and progesterone less than 800 pg/ml. During therapy, there was an improvement in menopausal symptoms, a decrease in luteinizing hormone (LH) and FSH levels, an increase in estradiol levels and the transdermal patches were well tolerated. At the end of therapy, 19 women continued to have regular ovulatory cycles with progesterone levels similar to those in luteal phase. FSH and LH concentrations were significantly lower than before therapy. This study shows that hormone replacement therapy not only improves menopausal symptoms but may also restore the hypothalamic-pituitary-ovarian function.