The effects of nomegestrol acetate on carbohydrate metabolism were investigated in 20 premenopausal women presenting with menstrual disturbances. The progestogen was administered from day 5 to day 24 of the cycle, over six consecutive cycles, at a dosage (5 mg/d) known to inhibit ovulation. A 3 hour oral glucose tolerance test (OGTT) was performed prior to the hormonal intake and at 3 months and 6 months of therapy. Blood glucose and insulin were measured before and for 3 hours after a 75 g glucose load, and the glucose and insulin areas under the curves (AUC) were calculated. The fasting glycosylated hemoglobin and fructosamine were also determined. Treatment did not induce any significant changes in plasma glucose or insulin glucose values during the oral glucose tolerance test, in glucose and insulin areas under the curves or in glycosylated protein levels. Two women with impaired glucose tolerance were not worsened during therapy. These data suggest that nomegestrol acetate is free from adverse effects on glucose tolerance after 6 months treatment.