Pelvic venous congestion is a common cause of chronic pelvic pain in women of reproductive age. Although this condition represents a functional disturbance of the pelvic circulation which is related to the menstrual cycle, its aetiology remains unknown. Indirect techniques demonstrate that the vasoconstrictive reflex response of the microcirculation of the foot to a rise in venous pressure is attenuated throughout the menstrual cycle. We wished to develop a simple and non-invasive direct measure of pelvic blood flow to aid diagnosis of this condition. Laser doppler blood flux measurements of the skin of the big toe and of the vaginal and rectal mucosa in the follicular and luteal phases of the menstrual cycle in 12 healthy asymptomatic premenopausal women (mean age 30 years) with regular cycles and in four healthy asymptomatic postmenopausal women (mean age 59 years) were carried out both in the supine position and in response to 40 degrees head-up tilt. The coefficient of variation of resting vaginal flux was lower for measurements in postmenopausal women (0.04) and in premenopausal women in the follicular phase (0. 07) compared with those in the luteal phase (0.16). At rest, vaginal blood flow was higher than rectal and skin flux in both premenopausal and postmenopausal women. In the follicular phase a decrease in flow was observed in response to head-up tilt in the skin (-32.0%), vagina (-34.3%) and rectum (-9.4%). In the luteal phase this reflex was attenuated at these three sites (-8.6%, +6.7% and +7.4% respectively). There were no significant reflex changes in postmenopausal women. Thus laser doppler fluximetry is a reproducible method for comparing the flux of blood in the microcirculation of the skin and of the vaginal and rectal mucosa. The skin is the least sensitive site for testing vascular reactivity in response to cyclical changes. The vaginal and rectal microcirculations are the most sensitive sites for testing visceral cyclical reactivity, and have the advantage of direct anatomical relevance. The follicular phase of the menstrual cycle is associated with greatest vascular reactivity and is the most appropriate phase during which to test for abnormal vascular responses.