Objective: To determine and evaluate the maternal serum thiol/disulfide homeostasis in pregnancies complicated by neural tube defects (NTD) via a novel method.Methods: Seventy-three pregnant women with NTD (study group) and seventy-one healthy control pregnant women (control group) were included in the study. A new and fully automated method was used to measure plasma native thiol, total thiol and disulfide levels, based on the reduction of dynamic disulfide bonds to functional thiol groups by sodium borohydrate.Results: The study and control groups were gestational age-matched. There were no statistical differences in demographic variables regarding age, gravidity, parity and body mass index. The serum native thiol levels (-SH) were 360.550.3 and 353.3 +/- 31.0mol/l in study and control groups, respectively, which was not statistically different (p=0.308). The native thiol/total thiol, disulfide/native thiol and disulfide/total thiol ratios were not statistically significantly different (p>0.05).Conclusion: Our preliminary results show that maternal serum thiol/disulfide homeostatis does not change in pregnancies complicated by NTD. Larger further studies are required to evaluate the relation of oxidative stress and development of NTD.