The aim of our study was to estimate the concentration of lipid peroxidation products and antioxidant system activity in cord blood and placental homogenates of 13 pregnant women with type I diabetes, 15 patients with gestational diabetes and 16 healthy pregnant women. Malondialdehyde (MDA) concentration, glutathione (GSH) content and the activity of CuZn superoxide dismutase (SOD) (Bioxytech, Oxis International S. A.) were measured. MDA and GSH levels increased significantly, whereas SOD activity was markedly diminished in diabetics, especially in these with type I, in comparison with the control group. Our results support the hypothesis that diabetic pregnant women and their fetuses/neonates are exposed to an increased oxidative stress. Moreover, we suggest that the measurement of oxidative stress level may be useful in clinical practice to assess fetus/neonate state and the risk of possible complications.