OBJECTIVE To examine the relationship between antioxidant status and T-cell activation in the pathogenesis of eclampsia by measuring the activities of erythrocyte catalase, an enzyme of antioxidant mechanism, and serum adenosine deaminase (ADA), regarded as a marker of T-cell activation. METHODS A total of 60 patients [20 eclamptic (E) pregnant women, 20 healthy pregnant (HP) women and 20 non-pregnant (NP) women] were included in the study. Maternal venous blood samples were obtained from each patient during weeks 28-37 of gestation, and biochemical analyses of catalase activity in erythrocytes and ADA activity in serum were carried out. RESULTS Erythrocyte catalase activity was significantly lower and serum ADA activity was significantly higher in the E pregnant women when compared with the HP women and NP women (P <0.001). No significant correlation was observed between erythrocyte catalase activity and serum ADA activity. CONCLUSIONS Erythrocyte catalase and serum ADA activities may at least in part contribute to the pathogenesis of eclampsia. However, more studies are needed to verify and clarify the relationship between antioxidant status and T-cell activation in eclampsia.