It is proposed that abnormalities of glucose and insulin metabolism have a role in both the aetiology and the clinical course of hypertension. There is resistance to insulin-stimulated glucose uptake in patients with hypertension, which is associated with glucose intolerance and hyperinsulinaemia. Hyperinsulinaemia could contribute to hypertension by stimulating the activity of the sympathetic nervous system and kidney sodium and volume reabsorption. Glucose intolerance and hyperinsulinaemia have been identified as risk factors for coronary artery disease, and their presence may help explain why the frequency of this disease has not been reduced by treatment of hypertension. The fact that several antihypertensive drugs deleteriously affect glucose, insulin, and lipid metabolism makes it even more important to consider these factors in the treatment of high blood pressure.