The purpose of this study was to evaluate the efficacy of methyldopa in the treatment of preeclamptic patients. This study was performed on 24 preeclamptic women who were in between 25-36 weeks of gestational age. 24 healthy pregnant women were taken as control group. Before starting treatment, 24 preeclamptic patients were examined with Doppler ultrasound. Pulsatility index, resistance index, systolic/diastolic ratio of uterine, umblical and fetal middle cerebral arteries were measured. Preeclamptic patients were treated with totally 1 g methyldopa per day. After 7 d, patients were reexamined with Doppler ultrasound. The effect of methyldopa on uterine, umblical and fetal middle cerebral artery blood flows were detected. Only one control with Doppler ultrasound was done to the healthy pregnant women. Before methyldopa treatment to the preeclamptic women, pulsatility index (PI), resistance index (RI) and systolic/diastolic ratio (S/D) on uterine and umblical arteries were significantly higher than the control group. However, fetal middle cerebral artery (MCA) values were significantly lower than the control group. When Doppler results of preeclamptic patients before and after the methyldopa treatment were compared, no significant differences in terms of Pulsatility Index, Resistance IndexI and S/D ratio of umblical and fetal middle cerebral arteries were found. However, the results of uterine artery were significantly lower after the treatment in preeclamptic patients. Treatment with methyldopa lowered the uterine artery resistance in preeclamptic patients but did not effect the resistance of umblical and fetal middle cerebral artery.