Estimation of the influence of oral supplementation with low dose of L-arginine on biophysical profile, foeto-placental circulation and neonatal outcome in preeclampsia. Randomized, placebo-controlled, double-blind, clinical trial. Oral therapy with 3 g of L-arginine daily or placebo as a supplement to standard therapy. Eighty-three preeclamptic women, randomly assigned to the L-arginine (n=42) or placebo (n=41) groups; [n=30 (L-arginine) and n=31 (placebo) ended the study, respectively]. Foetal gain chances due to ultrasound biometry, biophysical profile, Doppler velocimetry of pulsatility indices of umbilical and middle cerebral arteries, cerebro-placental ratio, as well as differences in duration of pregnancy and clinical data of newborn. L-arginine treatment transitory accelerated foetal gain and improved biophysical profile. Starting from 3rd week of therapy, the umbilical artery pulsatility indices values were significantly lower in L-arginine than in placebo group. Moreover, treatment with L-arginine caused significant increase of middle cerebral artery pulsatility indices and cerebro-placental ratio values. Latency was longer in L-arginine group. Neonates delivered in the L-arginine group revealed higher Apgar score. Supplementary treatment with oral L-arginine seems to be promising in improving foetal well-being and neonatal outcome as well as in prolonging pregnancy complicated with preeclampsia. However, these benefits require confirmation in more-powered, larger studies.