We measured plasma cortisol concentrations following breakfasts of different fat:carbohydrate ratio in 23 healthy subjects. A meal-related peak of plasma cortisol concentration was not found, as well as any difference in plasma cortisol levels following the two meals. Since the two meals elicited plasma glucose and plasma insulin levels which were significantly different, it is suggested that plasma cortisol is not acutely affected by ambient glucose and insulin concentrations. The same results were found when the study group was subdivided in nonobese (n = 13) and obese (Body Mass Index greater than n = 10), thus confirming the previous statement in the presence of different body weights.