OBJECTIVE To measure the flow velocity of the uterine and ovarian arteries through the menstrual cycle to determine there are changes. METHODS Serial measurements throughout the menstrual cycle in women attending an infertility clinic, compared with volunteers coming for annual examinations. Transvaginal ultrasound-color flow Doppler was the investigative tool. METHODS A University Hospital ambulatory care center. METHODS One hundred infertile women compared with 150 women attending the clinic for annual checkups. METHODS Changes in the resistance index of flow velocity waveforms of the uterine and ovarian arteries. RESULTS Uterine flow velocity has a resistance index of 0.88 +/- 0.04 (2 SE) in the proliferative phase and starts to decrease the day before ovulation. A nadir of 0.84 +/- 0.04 is reached on day 18 and remains at that level for the rest of the cycle. In anovulatory cycles, these changes do not occur. A subgroup of 12 women who lacked end diastolic flow in the uterine arteries during the secretory phase were identified. Eleven of these women were infertile, 8 of whom with primary infertility. Ovarian artery flow velocity is usually detected when the dominant follicle reaches 12 to 15 mm. The resistance index is 0.54 +/- 0.04 and also declines on the day before ovulation. A nadir of 0.44 +/- 0.04 is reached 4 to 5 days later and slowly rises to 0.050 +/- 0.04 before menstruation. CONCLUSIONS There are changes in the flow velocity patterns of the uterine and ovarian arteries during the normal ovulatory menstrual cycle. Because these changes in flow velocity begin before ovulation, it can be suspected that they may involve angiogenesis as well as hormonal factors. The changes noted in these studies are statistically significant but may be too small to be used as a diagnostic tool in the study of infertility problems.