SUMMARY1. In renal wrap hypertension in the rabbit and in essential hypertension in humans, non‐autonomic components of resistance are the major factors contributing to elevated blood pressure.2. The central nervous system plays an important role in moment to moment blood pressure control but is not responsible for maintenance of elevated pressure in essential hypertension.3. Specific regions of the brain‐stem maintain vascular tone through the effects of bulbospinal neurones which are organized both topographically and by chemical content.4. Structural wall thickening in resistance vessels in hypertension is a manifestation of an abnormality of a growth controlling process.5. Although several structural muscle growth factors have been identified, it is likely that only a few regulatory processes are critical.6. Future studies in hypertension should examine associations between genetic markers of medial thickening and environmental influences.