The aim of the present study was to compare insulin sensitivity and catecholamine responses to insulin in lean, hypertensive (HT) and normotensive (NT) premenopausal women. HT (BP 149 5/99 +/- 2 mmHg, n = 14) and NT (BP 128 +/- 4/81 +/- 2 mmHg, n = 12) were matched for age (46 +/- 1 vs. 47 +/- 1 years) and body mass index. Insulin sensitivity was determined by fasting serum insulin, glucose disposal rate (GDR) and insulin sensitivity index (GDR/I) using euglycemic hyperinsulinemic glucose clamp technique. Sympathetic nervous system activity was assessed by plasma adrenaline and noradrenaline in arterialized venous blood at baseline and during euglycemic hyperinsulinemic glucose clamp. Insulin sensitivity index correlated negatively with total cholesterol in HT (r = -0.57, p < 0.05) and with body mass index (r = -0.42, p < 0.05, n = 26). The response in catecholamines to euglycemic hyperinsulinemia in HT differed from NT with an increase both in noradrenaline and adrenaline. Blood pressure and heart rate responses, however, did not differ between HT and NT. Fasting serum glucose did not differ between the two groups (4.7 +/- 0.1 mmol/l in HT vs. 4.9 +/- 0.1 mmol/l in NT), nor did fasting serum insulin (16 2 mU/l vs. 13 mU/l). Glucose disposal rate (8.8 +/- 0.5 vs. 8.7 +/- 0.7 mg kg-1 body weight min-1) and insulin sensitivity index were similar (7.3 +/- 0.8 vs. 7.6 +/- 0.8 arbitrary units). We conclude that in lean, premenopausal hypertensive women insulin sensitivity is not reduced compared with age- and weight-matched normotensive women, but the hypertensives respond to hyperinsulinemia with increased plasma catecholamines, i.e. sympathetic nervous systemic activity. Also, insulin sensitivity correlates negatively with serum cholesterol. Thus, an insulin-hyperadrenergic interaction may possibly be involved as a pathogenetic factor in lean hypertensive women.