Oxidative stress occurs when cellular levels of reactive oxygen species exceed anti-oxidant capabilities and has been implicated in the pathogenesis of pre-eclampsia. In this study we have examined the tissue levels of endogenous anti-oxidant proteins (superoxide dismutase, glutathione peroxidase, thioredoxin reductase and thioredoxin) and the level of lipid and protein oxidation in placental samples from normal and pre-eclamptic pregnancies. Pre-eclamptic tissue homogenates demonstrated significantly increased levels of lipid peroxidation ( protein versus protein, P<0.001) and a trended increase in protein carbonyl concentration ( protein versus protein) when compared to controls. The levels and activities of the anti-oxidant proteins superoxide dismutase ( protein versus protein, P<0.02), thioredoxin reductase ( protein versus protein, P=0.02), thioredoxin ( protein versus protein, P=0.02) and glutathione peroxidase ( protein versus , P<0.02) were all found to be significantly reduced when comparing pre-eclamptic placental tissue homogenates to gestational age-matched control placentae from non-pre-eclamptic pregnancies. The results of this study demonstrate a decreased enzymatic anti-oxidant capacity and increased oxidation in placental tissue from pre-eclamptic women, which may contribute to the pathogenesis of this complex disorder.