We measured plasma concentrations of asymmetric dimethylarginine (ADMA), endothelin-1 (ET-1), soluble vascular cell adhesion molecule-1 (sVCAM-1) and E-selectin in 56 patients with gestational diabetes (GDM), 68 pregnant women with normal glucose tolerance (NGT) and 36 healthy non-pregnant women. ADMA concentrations were markedly lower in NGT [0.48 (0.42-0.55) micromol/l] than in GDM subjects [0.50 (0.43-0.67) micromol/l] and healthy controls [0.57 (0.46-0.72) micromol/l, P = 0.005]. ET-1 levels were comparable between GDM [0.76 (0.58-0.90) pg/ml] and NGT women [0.75 (0.63-0.92) pg/ml] and significantly higher than in the non-pregnant subjects [0.62 (0.52-0.72) pg/ml, P = 0.007 and P = 0.005, respectively]. There were no differences in sVCAM-1 and E-selectin levels between the groups studied. ADMA levels were significantly associated with fasting glucose (beta = 0.23, P = 0.02) and gestational age (beta = 0.24, P = 0.01). Our results suggest that physiological adaptation to pregnancy is associated with a fall in circulating ADMA and an elevation of ET-1 concentrations, irrespective of the disturbances of glucose tolerance.