The possible correlations between the increase in cortisol levels and the decrease in glucose tolerance and changes in insulin and glucagon secretion in normal pregnancy were studied in 17 normal pregnant women. Total and free plasma cortisol concentrations and urinary cortisol excretion rate were measured monthly from wk 12 and the results were related to the changes in glucose tolerance in early, mid, and late pregnancy and finally compared to postpartum findings. In early pregnancy, total and free plasma cortisol concentrations and the urinary cortisol excretion rate were already higher than postpartum and the levels increased further throughout gestation, reaching maximum levels at term. Glucose tolerance deteriorated during pregnancy. When the increases during pregnancy in total and free plasma cortisol concentrations and urinary cortisol excretion rates were related to the deterioration of glucose tolerance, significant positive correlations were obtained (r-values between 0.55 and 0.63, P < 0.05). No correlation was found between the increase in cortisol levels or excretion rates and the changes in the insulin and glucagon responses to glucose in pregnancy. The elevation of cortisol levels in pregnancy might possibly be associated with the diabetogenicity of pregnancy.