OBJECTIVE Oxidative stress has been implicated in pregnancy-induced hypertension and preeclampsia. There is still some debate over whether this is confined to the placenta or occurs in the maternal circulation. This study was designed to investigate this question by comparing parameters of oxidative stress in samples of maternal blood and cord blood taken from normotensive and hypertensive pregnant women. A further aim was to compare these parameters in maternal milk from the two populations. METHODS Forty-six hypertensive (31 preeclamptic and 15 chronic hypertensive) and 60 normotensive pregnant women were recruited. Antecubital blood was collected from each woman before and after delivery, cord blood just after delivery, and maternal milk for the first 3 days postpartum. Total antioxidant capacity, total peroxides and sulphydryl concentration were measured and total antioxidant capacity calculated for each specimen. RESULTS For all specimens (maternal blood plasma, cord blood plasma, maternal milk) total antioxidant capacity and sulphydryl concentration were significantly lower in the hypertensive women than in the normotensive, while total peroxide and oxidative stress index were significantly higher. CONCLUSIONS These results support the association between hypertension in pregnancy and oxidative stress and the view that this occurs throughout the maternal circulation. They show further that oxidative stress may be transmitted from mother to newborn in maternal milk. Supplementation with antioxidants could, in view of our findings, possibly provide protection to the mother and fetus and also, through transmission in maternal milk, to the newborn.