Abstract. Introduction: While increased oxidant stress is implicated in a variety of maternal and neonatal complications, the effects of tobacco-induced alterations in systemic redox status remains clinically unrecognized. We hypothesized that maternal smoking would increase systemic oxidant stress during pregnancy in the otherwise healthy female. Methods: We evaluated plasma samples from 212 post partum women as part of a larger parent investigation of mother-infant pairs. An extensive maternal interview noted tobacco, alcohol, cocaine or marijuana use throughout the pregnancy. The redox pairs of glutathione/oxidized GSSG and cysteine/oxidized cystine were measured in the plasma by high performance liquid chromatography. Results: Over 64.5% of the sample reported tobacco use during pregnancy. Tobacco-exposed newborns demonstrated lower birth weight, decreased head circumference and birth length. Maternal tobacco use decreased maternal cysteine by 10% and cysteine/cystine redox potential was dramatically oxidized by >20mV, independent of alcohol, marijuana or cocaine use. Conclusion: Significant oxidation of maternal cysteine/cystine redox pair occurred before clinically apparent decreases in newborn birth weight. We concluded that tobacco use during pregnancy was associated with significant oxidation of the cysteine/cystine redox pair in the otherwise healthy post partumwomen. The implications of unrecognized derangements of systemic redox on the health of the mother and infant require evaluation.