In nondiabetic hypertensive subjects, a relationship has been found between insulin resistance and level of blood pressure. Since type II (non-insulin-dependent) diabetic subjects are often both insulin-resistant and hypertensive, we studied the relationship between insulin resistance and blood pressure level in a group of patients with type II diabetes. Fourteen women and 19 men with diabetes for 2 to 14 (mean, 7.4) years, treated with diet alone (five subjects) or combined with hypoglycemic agents, were studied. Their average hemoglobin A1c (HbA1c) levels during the study period were 6.6% to 11.7% (mean, 8.6%), and their body mass indexes (BMI) were 20.8 to 33.1 (mean, 26.3) kg/m2. Insulin sensitivity was measured using the hyperinsulinemic, euglycemic glucose clamp technique, and an insulin-sensitivity index was calculated as the ratio of the glucose disposal rate (GDR) to the insulin concentration during clamp (GDR/I). The average of three to eight measurements of diastolic blood pressure (DBP) during the study period (9 to 24 months) in each subject was 79 to 111 (mean, 95.1) mm Hg, and DBP also showed significant correlations to BMI (r = .54) and fasting C-peptide level (r = .38). In a multiple regression model, GDR/I, antihypertensive treatment, and known duration of diabetes were significant and independent predictors of variations in blood pressure, and GDR/I could account for 35% of the observed variations in DBP. We conclude that, in accordance with what has been found in nondiabetic hypertensives, DBP correlates significantly to insulin resistance in type II diabetic subjects.