DESCRIPTION Physiological levels of nitric oxide (NO), a product of endothelial cells and the syntrophoblast, play an important role in pregnancy by regulating maternal blood pressure and ensuring placental perfusion. However, in response to inflammatory cytokines, NO increases its level, becomes pro-oxidant and produces a variety of potentially toxic biochemical reactions as, for example, nitration, nitrosation and oxidation. One of these reactions, the reaction of superoxide radical and NO, forms a peroxynitrite yielding a stable nitration product of tyrosine. The nitrated protein can be used as a marker for sites of acute and chronic inflammation, and has been observed in sepsis and preeclampsia. It is proposed that in patients with infection of fetal/maternal tissues (chorioamnionitis/deciduitis), nitration of placental proteins may lead to preterm labor and delivery. The hypothesis to be tested is that pre-term delivery is associated with nitration reactions. Thus, placentas from pre-term deliveries (less than 32 weeks of pregnancy) will be evaluated for tyrosine nitration. A companion study will attempt to characterize the specific proteins that undergo tyrosine nitration.