Abstract Objectives: The aim of the study was to assess the relationship between maternal and umbilical cord plasma concentrations of endothelin 1 (ET-1) and cyclic guanosine monophosphate (cGMP) in women with diabetes mellitus (DM). Material and methods: The study was performed on 19 neonates of women with pregestational DM, 23 neonates of women with gestational diabetes (GDM), and 18 neonates of healthy, uncomplicated pregnancies. Results: We found that umbilical and maternal ET-1 and cGMP concentrations in pregestational DM or GDM women were not changed in comparison with the controls. In women without DM, positive correlations between maternal (r=0.64; p<0.005) and umbilical cord plasma (r=0.60; p<0.009) ET-1 and cGMP concentrations were found. However, in pregnancies complicated by pregestational DM or GDM such associations were not observed. Conclusions: Umbilical and maternal plasma concentrations of ET-1 and cGMP in pregnant women with pregestational diabetes as well as gestational diabetes were not changed in comparison with the non-diabetic women. In women without DM maternal and umbilical cord plasma ET-1 and cGMP concentrations showed positive correlations. In pregnancies complicated by pregestational DM or GDM maternal and umbilical cord plasma ET-1 and cGMP concentrations were not interdependent.