SUMMARY1. Hypertrophy of vascular and cardiac smooth muscle is present in human primary hypertension. The amplifier properties associated with hypertrophy play a major role in maintaining hypertension.2. Long‐term antihypertensive drug therapy causes substantial regression of the structural changes, assessed by the non‐autonomic component of vascular resistance, and by left ventricular mass. The latter occurs more slowly.3. The more complete the reversal of left ventricular hypertrophy, the more slowly hypertension redevelops if long‐term antihypertensive therapy is discontinued.4. Subjects who redevelop hypertension more rapidly tend to have higher cardiac output, suggesting that the cardiac amplifier may play a role in the pathogenesis.5. Studies of small arteries and of veins from patients with primary hypertension suggest that there may be a general disturbance of vascular smooth muscle function, independent of the mechanical effects of elevated systemic blood pre