Pre-eclampsia is a pregnancy-related multisystem disorder characterised by elevation of blood pressure and proteinuria, in which oxidative stress may play an important role. Blood pressure is partly controlled by O(-)(2) production by NADPH/NADH oxidase and recently it was shown that a C242T substitution in the p22phox gene was associated with coronary artery disease, in which elevated blood pressure and oxidative stress are also important pathophysiologic features. Therefore we studied the prevalence of the C242T polymorphism in the NADPH/NADH oxidase gene in women with pre-eclampsia and/or haemolysis, elevated liver enzymes and low platelets (HELLP) syndrome as compared with women with a normotensive pregnancy. DNA from control women (n = 78), women with pre-eclampsia (n = 40), HELLP syndrome (n = 9) or women with HELLP complicated by pregnancy-induced hypertension or pre-eclampsia (n = 46) were tested for the presence of the C242T polymorphism by polymerase chain reaction followed by restriction fragment-length polymorphism. The prevalence of the homozygous CC-genotype was similar in the patient groups compared with controls. The allele frequency of the T-allele was 31% in both control and patient groups. In conclusion the C242T polymorphism in the p22phox subunit of the NADPH/NADH oxidase gene is not associated with pre-eclampsia. Therefore, oxidative stress generated by NADPH/NADH oxidase probably does not play a role in the development of pre-eclampsia.