Circulating insulin levels are elevated in many study patients with hypertension, and more sophisticated studies suggest that these elevations indicate tissue resistance to insulin action. The main site of this defect appears to be insulin action on glycogen synthesis activity in skeletal muscle. Insulin resistance may be seen in early life, even in the normotensive children of hypertensive parents. Experimental renovascular and deoxycorticosterone acetate-salt hypertension is not associated with insulin resistance. The Dahl salt-sensitive rat is insulin resistant. Conflicting results have been obtained in the spontaneously hypertensive rat. Insulin is primarily a vasodilator in skeletal muscle but also selectively stimulates the sympathetic nervous system without elevating blood pressure. Insulin resistance in hypertensive patients has been linked to elevated erythrocyte sodium-lithium countertransport. Insulin resistance and hypertension appear to coassociate frequently and may have common genetic and environmental antecedents.