Although oxidative stress has been implicated in the pathogenesis of type 2 diabetes, limited data are available regarding its role in gestational diabetes mellitus (GDM), a disease of similar pathophysiology. The proinflammatory cytokines TNFa, IL-6, and IL-8 are released from the placenta at term and have been implicated in and/or associated with various metabolic events, including decreased insulin sensitivity. Previously we reported differences in the ex situ release of proinflammatory cytokines from placental and adipose tissues obtained from women with and without GDM. We proposed that these differences reflect preexposure and/or adaptation to oxidative stress by GDM tissues. In this study, we tested the hypothesis that placental tissue from women with GDM is less responsive to oxidative stress than tissue from normal women. Under basal conditions, release of TNFα, IL-6, and IL-8 was similar in both control and GDM groups. However, 8-isoprostane release was 2-fold greater in the GDM group (P < 0.01). In response to oxidative stress, TNFα and 8-isoprostane release and nuclear factor-κB (NF-κB) DNA-binding activity were significantly increased in normal tissues (20-fold, 2-fold, and 35%, respectively, P < 0.01). In contrast, the response of GDM tissues to oxidant stress was blunted, with no change in 8-isoprostane release, a 4-fold increase in TNFa release, and a 40% reduction in NF-κB DNA-binding activity. These data support the hypothesis that placentae from women with GDM display a reduced capacity, mediated by repression of NF-κB activity, to respond to oxidative stress.