Preeclampsia (PE) is a syndrome expressing a pregnancy disorder of high prevalence associated with maternal-fetal morbidity and mortality. Although the etiology of PE remains elusive, oxidative stress and endothelial dysfunction have been involved in the mechanism of production of the clinical manifestations of the syndrome. At present, there is no satisfactory treatment to prevent the development of PE, except to follow some measures to avoid or reduce complications, being early delivery the only successful treatment in severe PE. Recent studies have given some clues about the importance of nitric oxide (NO) in the pathophysiology of PE. During pregnancy, NO is one of the most important relaxing factors of myometrium and also plays a key role in the control of blood flow in uterus and placenta. In PE, the bioavailability of NO is decreased compared with normal pregnancy. It is postulated that this alteration is due to decreased NO half life, rather than to an impairment in eNOS activity. Deficit of substrates and increased reactive oxygen species might contribute to the decrease in NO bioavailability. Accordingly, plasma L-arginine levels have been reported lower in women with PE than those in normal pregnancy. In this study, we provide evidence supporting the view that L-arginine supplementation in early pregnancy might reduce the occurrence of PE.