Summary. Preeclampsia, a pregnancy-specific syndrome characterized by hypertension, proteinuria and edema, resolves on delivery of the placenta. Normal pregnancy is itself characterized by systemic inflammation, oxidative stress and alterations in levels of angiogenic factors and vascular reactivity. This is exacerbated in preeclampsia with an associated breakdown of compensatory mechanisms, eventually leading to placental and vascular dysfunction. The underlying pathology of preeclampsia is thought to be a relatively hypoxic or ischemic placenta. Both the placenta and maternal vasculatures are major sources of reactive oxygen and nitrogen species which can interact to produce peroxynitrite a powerful prooxidant that covalently modifies proteins by nitration of tyrosine residues, to possibly alter vascular function in preeclampsia. The linkage between placental hypoxia and maternal vascular dysfunction has been proposed to be via placental syncytiotrophoblast basement membranes shed by the placenta or via angiogenic factors which include soluble flt1 and endoglin secreted by the placenta that bind vascular endothelial growth factor (VEGF) and placental growth factor (PIGF) in the maternal circulation. There is also abundant evidence of altered reactivity of the maternal and placental vasculature and of the altered production of autocoids in preeclampsia. The occurrence of preeclampsia is increased in women with preexisting vascular disease and confers a long-term risk for development of cardiovascular disease. The vascular stress test of pregnancy thus identifies those women with a previously unrecognized at risk vascular system and promotes the development of preeclampsia. Preexisting maternal vascular dysfunction intensified by placental factors is possibly responsible for the individual pathologies of preeclampsia.