To investigate the relationship between insulin resistance and electrocardiographic changes in hypertension in the absence of confounding influences, plasma glucose and insulin responses to oral glucose were studied in 26 normotensive and 38 hypertensive subjects. Resting ECG was taken and classified into normal or abnormal using the Minnesota code. Among the 38 subjects, 16 had ECG abnormalities. All the hypertensive subjects had normal glucose tolerance. Serum insulin response of hypertensive subjects with ECG changes was 43% higher than those of hypertensive subjects without ECG changes and of normotensive subjects. The ratio AUC glucose/AUC insulin, a measure of insulin sensitivity was significantly reduced in subjects with abnormal ECG. Serum LDL cholesterol was significantly elevated and was the highest in hypertensive subjects with abnormal ECG. The ratio, Total Cholesterol/HDL Cholesterol was elevated to 5.81+/-0.47. I(125)-insulin binding to erythrocytes from 6 normotensive subjects, and 16 hypertensive subjects (8 with and 8 without ECG abnormalities) indicated 50% reduction in insulin receptor number in both the groups of hypertensive subjects compared to normotensive subjects. Multiple logistic regression analysis using mean blood pressure, serum total cholesterol, LDL cholesterol/HDL cholesterol, sex, insulin level at 60 min in OGTT, treatment, serum triglyceride, presence of family history of diabetes, CHD, hypertension and tobacco as independent variables causing ECG changes, revealed correct classification in 84% of cases. Among the variables, insulin level in OGTT contributed the most to ECG abnormalities. The data suggest that in the non obese, non diabetic Asian Indian hypertensive subjects, the presence of electrocardiographic abnormalities might be partly related to hyperinsulinemia or insulin resistance in them.