Aim: Assymetric dimethylarginin (ADMA), an inhibitor of nitric oxide synthase (NOS), has been linked to endothelial dysfunction. Our aim in this study was to compare ADMA and arginine levels in normal glucose tolerance, impaired glucose tolerance and gestational diabetes groups and investigate the effect on baby birth weight. Material and Method: Serum ADMA and arginine levels were investigated in 64 patients whose 50-g glucose loading test was normal (group 1, NGT); 33 patients whose 50-g test result was high and those whose 100-g oral glucose tolerance test (OGTT) was normal, namely, those with impaired glucose tolerance (IGT, group 2); and in 8 patients diagnosed with gestational diabetes mellitus (GDM, group 3). Results: Arginine levels were significantly higher in the IGT group than in the NGT group. ADMA levels were high in the GDM group, but the difference was not statistically significant. There were a statistically significant correlation between arginine and ADMA levels and the ADMA level of those with a diabetes history. No significant relationship was found between ADMA level, arginine and the weight of the infant. Discussions: Although there has not been a clinical status related with nitric oxide deficiency caused by increasing ADMA concentrations, pregnancies with increased body mass indeks (BMI), family history for diabetes and older ages should be carefully monitorized. ADMA tends to increase in patients with IGT and GDM. In addition, blood ADMA and arginine levels do not seem to influence the weight of the infant.