Objective. Alteration of cytokines level and oxidative stress are both associated with preeclampsia (PE). We have investigated if IL-6 and IL-18 levels were related to coenzyme Q10 (CoQ10), an antioxidant and a marker of oxidative stress in the plasma from normotensive and preeclamptic pregnancies. Design. IL-6 and IL-18 levels were determined by enzyme-linked immunosorbent assays in plasmas from preeclamptic (n = 29) and normotensive pregnancies (n = 30). The concentrations of CoQ10 in the different redox forms were measured in plasma using liquid chromatography coupled to electrochemical detection. Data were analyzed using the Wilcoxon Rank-Sum test and correlations were obtained by the Spearman's Rho test. Main outcome measures. IL-6 concentrations were 2.8-fold higher in preeclamptic plasmas than in controls (p = 0.0006), and IL-18 concentrations were found significantly lower in preeclamptic samples than in controls (p = 0.007). No correlation was found between IL-18 or IL-6 and antioxidant vitamin CoQ10 in plasmas from normotensive pregnant women. However, in PE, IL-18 level was positively correlated with the reduced form of CoQ10 (r = 0.3680, p = 0.0495). Conclusion. This is the first demonstration that IL-18 is potentially linked to oxidative stress in PE, since its level correlates with the concentration of the powerful antioxidant CoQ10. These results also associate the immune system with the oxidant/antioxidant imbalance observed in PE.