SummaryBackground: Birth involves strong oxidative stress for the infant, implying an increased production of free radicals. The aims of this study were to assess the antioxidant response to oxidative insult at birth, by estimating the superoxide dismutase (SOD) and glutathione peroxidase (GPX) activity in umbilical cord blood, and to evaluate their dependency on the degree of maturation of the newborns. Methods: In the present study, 60 preterm infants (study group) as well as a full-term healthy reference group (A=53) were included. Additionally, the preterms were divided in 3 groups according to their condition at the end of the 1st week of life: preterm control (B=25), on oxygen support (C=18), and ventilated group (D=17). Results: The obtained results indicate markedly lower antioxidant capacity of the preterm infants: they had significantly lower SOD and GPX activity than the full-term infants (p<0.001, for both). Investigated antioxidants also showed significant differences between the groups of preterms. SOD activity was higher in preterms with postnatal respiratory failure compared to preterm control (p<0.001). On the contrary, GPX activity was decreased in the oxygen supported group (10%) and even more in the ventilated group (28.5%) (p<0.001, for both). The newborns enzyme activities were also profoundly modulated by the gestational age and birth weight, specifically the GPX.