Uterine artery blood flow was analyzed in 8 menopausal women receiving hormonal replacement therapy consisting of transdermal E2 (0.05 mg/24 h) administered without interruption for 12 weeks in combination with a cyclical supply of Nomegestrol acetate (5 mg/24 h) for the last 13 days of each four week treatment cycle. Uterine artery flow was analyzed using transvaginal pulsed Doppler making semi quantitative measurements of Doppler flow waves by calculation of the pulsatility index (PI). Before treatment (baseline) uterine artery PI was elevated at 3.7 +/- 0.7 (mean +/- SD) and decreased significantly under the influence of E2 to reach 1.9 +/- 0.8 after 2 weeks of treatment. This effect of E2 was not altered by the cyclical addition of Nomegestrol acetate. On the 3rd month of treatment, uterine artery PI values were lower than seen during the first month and no difference was observed between measurements made while receiving E2 (week 10) or E2 and Nomegestrol acetate (week 12). These data indicate that cyclical administration of the progestin Nomegestrol acetate does not interfere with the vascular effects of E2 lowering the uterine artery PI a reflector of the impedance to flow.