The authors studied the effect of healthy aging on the cardiovascular homeostatic mechanism in premenopausal and postmenopausal women with similar estrogen levels. 12 healthy postmenopausal women, confirmed by follicular-stimulating hormone (FSH) and luteal hormone (LH) levels, were compared with 14 normally menstruating women during the early follicular phase (young-EF), to avoid as much as possible the effects of estrogen. Systolic BP was 108+/- 1.5 vs 123 +/- 2.5, supine norepinephrine was 260 +/-30 vs 216+/-45 and upright 640+/-100 vs 395+/-50 pg/ml in young-EF vs postmenopausal, respectively. Vagal cardiac tone indices decrease significantly with aging. The authors conclude that in young women, parasympathetic control is the main regulator of the cardiovascular system and in postmenopausal women, sympathetic tone dominates.