1. Eighty-six apparently healthy postmenopausal women not receiving hormone replacement therapy were given an intravenous glucose tolerance test. Plasma glucose, insulin and C-peptide concentrations were determined in fasting and post-glucose challenge samples. 2. Using a multivariate regression model, with predictor variables of chronological age, menopausal age and body mass index, neither chronological age nor menopausal age correlated with fasting or post-challenge plasma glucose or C-peptide concentrations. In contrast, menopausal age was positively associated with fasting plasma insulin concentration ( P = 0.038, model r 2 = 0.107), insulin area ( P = 0.01, model r 2 = 0.236) and incremental insulin area ( P = 0.024, model r 2 = 0.243). This relationship could not be explained by differences in lifestyle variables of alcohol consumption, physical activity, previous duration of oral contraceptive usage, history of cigarette smoking or body mass index. 3. Our findings suggest that loss of ovarian function is associated with hyperinsulinaemia, possibly via alterations in the clearance of circulating insulin from the plasma. The hyperinsulinaemia observed may contribute to the increased risk of cardiovascular disease seen in postmenopausal women.