Objective:To assess the uterine hemodynamics in gestational trophoblastic tumors and to correlate them with response to chemotherapy.Methods:Using transvaginal color Doppler ultrasound, we measured the peak systolic velocity and the resistance index (RI) of the uterine arteries in 23 women with gestational trophoblastic tumors before each course of chemotherapy. Fifty‐five nonpregnant women and another 15 women who had uneventful molar evacuation were enrolled as controls. Two‐tailed Studentttest was used for statistical analysis.Results:A hyperdynamic uterine circulation was noticed at diagnosis in all gestational trophoblastic tumors, manifested as higher peak systolic velocity (mean ± standard deviation 57.5 ± 20.4 cm/second) of the uterine arteries compared to nonpregnant (28.3 ± 3.41 cm/second;P< .0001) and uneventful post‐mole uteri (26.8 ± 3.08 cm/second;P< .0001). The RI values of the uterine arteries in gestational trophoblastic tumors at diagnosis ranged from 0.21‐0.80. However, the mean value (0.56 ± 0.19) was lower than those of nonpregnant (0.80 ± 0.05;P< .0001) and post‐mole uteri (0.75 ± 0.06;P< .0001). A higher pre‐treatment uterine artery RI (mean 0.71 ± 0.09) was noted in ten patients with gestational trophoblastic tumors requiring fewer than five courses of chemotherapy, compared with the mean in 13 patients requiring longer courses of treatment (0.47 ± 0.14;P< .0001). There was a marked decrease of peak systolic velocity during the first three courses of treatment in the former group (54.2 to 23.6 cm/second;P< .001), in contrast to no change in the latter group (60.1 to 60.5 cm/second).Conclusion:Uterine hemodynamic characteristics assessed by color Doppler ultrasound might predict and monitor the response to chemotherapy in gestational trophoblastic tumors.(Obstet Gynecol 1994;83:1021‐5)