The present study assessed the possible role of oxytocin in the deterioration of glucose tolerance in gestational diabetes. Plasma levels of oxytocin, insulin, glucagon and glucose were measured at the time of a 400-kcal breakfast meal tolerance test in 12 women with gestational diabetes and 12 normal pregnant women in the third trimester. The gestational diabetic women had higher basal levels of insulin and an enhanced, delayed and prolonged insulin response to the breakfast. The same differences occurred in the glucose levels. There was no significant difference in the glucagon levels between the two groups. In the normal pregnant women, a significant (p < 0.05) though small rise in glucagon levels occurred 30 min after the ingestion of the breakfast. Oxytocin levels were not affected by the breakfast, and there was no clear difference between the two groups. The metabolic differences between the normal pregnant and gestational diabetic women were not related to any differences in oxytocin levels. In conclusion, we found no evidence of a role of oxytocin in the alteration of glucose metabolism in women with gestational diabetes. However, since alterations in oxytocin levels of possible significance for an impaired glucose tolerance are found in type 1 diabetic and extremely obese patients, further studies are needed in women with gestational or manifest diabetes.