Uterine artery blood flow measurements made solely in the recumbent position may miss physiological changes that occur while patients are upright. We evaluated the effect of standing on the minute blood flow volume of the ascending uterine artery, the pulsatility index (PI), resistance index (RI) and waveforms and on the PI and RI of the myometrial spiral arteries and waveforms at 3-8 and at 9-14 min standing in 74 non-pregnant women. At 9-14 min, the uterine artery blood flow volume had decreased by an average of 34% and the RI had significantly increased in 70% of subjects. Decreased uterine artery blood flow volume was associated with increased distal resistance and with decreased vessel diameter, possibly due to stretching or kinking of the uterine arteries. Changes in the spiral artery PI paralleled changes in the uterine artery PI at 9-14 min, but were less pronounced. Spiral artery PI and RI were not related to the uterine artery blood flow volume while women were recumbent, although they were significantly related while women were standing. The effects of age, uterine mobility and uterine position on uterine artery or spiral artery blood flow were apparent only while women were standing. We conclude that standing as well as recumbent studies are necessary when uterine and myometrial blood flow are evaluated, and that uterine flow volume per minute should be measured whenever possible.