['To study the pathophysiological importance of changes in insulin sensitivity and islet function over time for alterations in glucose tolerance in a randomly selected large group of non-diabetic women aged 57-59 years over a 3-year period.', 'At baseline and at the 3-year follow-up, glucose tolerance (WHO 75 g oral glucose), insulin sensitivity (euglycaemic, hyperinsulinaemic clamp) and insulin and glucagon secretion (2 to 5-min responses to 5 g i.v. arginine at fasting, 14 and > 25 mmol/l glucose) were measured.', 'At baseline, women with impaired glucose tolerance (IGT, n = 28) had lower insulin sensitivity (p = 0.048) than normal women (NGT, n = 58). The arginine-induced insulin responses (AIR) were inversely associated with insulin sensitivity (r > or = -0.55, p < 0.001). When related to the 3-year follow-up, the baseline product of AIR at 14 mmol/l glucose times insulin sensitivity, insulin effect index (IE) (r = -0.40, p < 0.001) and the arginine-induced glucagon response at 14 mmol/l glucose (AGR, r = 0.28, p = 0.009) both correlated with follow-up 2-h glucose. In a multiple regression model, baseline 2-h glucose, insulin effect index and arginine-induced glucagon response independently predicted 2-h glucose at follow-up (total r = 0.668, p < 0.001). Furthermore, delta insulin sensitivity (i. e. follow-up minus baseline) correlated with delta insulin secretion (r = -0.30, p = 0.006), whereas delta glucagon secretion correlated with delta2-h glucose (r = 0.30, p = 0.006) over the 3 years. In a multiple regression, alterations in 2-h glucose over the 3 years were independently determined by changes in fasting insulin and glucagon secretion (r = 0.424, p < 0.001).'] Is glucose intolerance predicted by low insulin secretion and high glucagon secretion : outcome of a prospective study in postmenopausal Caucasian women?