Patients and Methods: 44 patients with a singleton pregnancy who had been referred for IUGR detected by ultrasonic examination were included. Vascular IUGR was defined by fetal abdominal circumference less than or equal to the third percentile, associated with abnormal uterine Doppler. After double blind randomization, patients received either 14 g/day of L-arginine (90 mL syrup, Veyron France Laboratories), or a placebo. Doppler ultrasound examination of the uterine, umbilical and cerebral circulation, and of ductus venosus was performed prior to inclusion, after 7 days of treatment, and the day before delivery. Ultrasound examination was performed upon randomization, and weekly until birth. Venous blood and urine samples were collected before initiation and after 7 days of treatment, and both maternal and umbilical venous samples were obtained at delivery for nitrate and nitrite (NO2-/ NO3-) determination.