Weekly serum β-hCG measurements and transvaginal ultrasound scans coupled with color Doppler flow were performed on 8 patients with hydatidiform mole. Two patients later developed persistent trophoblastic disease, necessitating chemotherapy. The correlation coefficients between Doppler flow indices, systolic-diastolic (S/D) ratio and pulsatility index (PI) with log β-hCG were ––0.96 and ––0.97, respectively. The weekly S/D and PI indices were plotted on an individual curve. Only the 2 patients who developed persistent gestational trophoblastic disease had PI index levels of < 1.5 as early as 2 weeks after molar evacuation. At that stage their serum β-hCG levels were not different from some of the other patients. In this preliminary report, the regression of the disease could be reliably assessed by observing the changes in low resistance flow which paralleled the gradual decrements in serial β-hCG levels. Thus, the contribution of this noninvasive imaging technique encourages the authors to further investigate Doppler flow monitoring among a larger sample of patients suffering from various gestational trophoblastic diseases.