Objective: To stabilise the disease process in women with early onset severe preeclampsia and/or HELLP syndrome by enhancing maternal antioxidants effects of glutathione. Study design: In a randomised, double-blind, placebo-controlled trial, women with severe preeclampsia and/or HELLP syndrome received oral N-acetylcysteine. Primary outcome measures were disease stabilisation expressed as treatment-to-delivery interval and biochemical assessment of glutathione and parameters of oxidative stress. Secondary outcome measures were maternal complications, rate of caesarean section, stay at intensive care unit, postpartum hospital stay and neonatal morbidity and mortality. Analyses were done by intention-to-treat using Wilcoxon’s two-sample test and regression analysis. Results: Median treatment-to-delivery interval was not significantly different between the N-acetylcysteine and placebo group. The whole blood and plasma levels of glutathione and other thiols were not affected by N-acetylcysteine administration, except for plasma homocysteine concentrations, which were lower in the N-acetylcysteine group. There were no differences found in maternal nor neonatal secondary outcome measures between both groups. Con-clusion: Oral N-acetylcysteine administration does not stabilise the disease process of early onset severe preeclampsia and/or HELLP syndrome. Objective: To stabilize the disease process in women with early onset severe preeclampsia and / or HELLP syndrome by enhancing maternal antioxidants effects of glutathione. Study design: In a randomized, double-blind, placebo-controlled trial, women with severe preeclampsia and / or HELLP syndrome received oral N-acetylcysteine. Primary outcome measures were disease stabilization expressed as treatment-to-delivery interval and biochemical assessment of glutathione and parameters of oxidative stress. Secondary outcome measures were maternal complications, rate of caesarean section, stay at intensive care unit Results: Median treatment-to-delivery interval was not significantly different between the N-acetylcysteine ​​and placebo group The whole blood and plasma levels of glutathione and other thiols were not affected by N-acetylcys teine ​​administration, except for plasma homocysteine ​​concentrations, which were lower in the N-acetylcysteine ​​group. There were no differences found in maternal nor neonatal secondary outcome measures between both groups. Con-clusion: Oral N-acetylcysteine ​​administration does not stabilize the disease process of early onset severe preeclampsia and / or HELLP syndrome.