The present study aimed at testing a possible relationship between hemorheologic factors such as hematocrit and whole blood viscosity, and insulin sensitivity in premenopausal, hypertensive (HT), and normotensive (NT) women. Fourteen HT and 12 NT women were studied with the hyperinsulinemic euglycemic glucose clamp technique. Insulin sensitivity was similar in NT and HT (8.7 +/- 0.8 v 7.6 +/- 0.8 arbitrary units). Whole blood viscosity did not differ between the two groups at any shear rate (shear rate 5.2 sec-1: 7.5 +/- 0.4 in NT and 8.0 +/- 0.3 in HT, P = NS). Statistically significant negative correlations were observed between the insulin sensitivity index and calculated whole blood viscosity at both high (r = -0.49, P < .01) and low shear rates (r = -0.50, P < .01, n = 26). Insulin sensitivity index was also negatively correlated to body mass index in the combined groups (r = -0.40, P = .04), and to both systolic and diastolic blood pressure (r = -0.44, P = .02 and r = -0.38, P = .05, respectively). In multiple regression analysis, whole blood viscosity, body mass index, systolic, and diastolic blood pressure accounted for 39% of the variation in insulin sensitivity index, but only whole blood viscosity was an independent explanatory variable for the insulin sensitivity index. These results suggest hemorheologic, and therefore indirectly hemodynamic factors as correlates to insulin sensitivity.