Nitric oxide (NO) is a potent vasodilator, considered to have major effects on gestational endothelial function.6 NO is synthesized by nitric oxide synthases (NOS), namely endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS.7 Studies investigating circulating levels of NO in preeclampsia have reported conflicting results.8 This is in contrast to studies that have shown that plasma from women with preeclampsia elicits reduced endothelium-dependent vasodilatation in isolated vessels. This evidence concerns the gene NOS1 and preeclampsia.