1. Long-term changes in the function and structure of arteries and veins in response to an elevation in arterial pressure have been studied in the rabbit after partial abdominal aorta constriction.
2. Transient changes occur in the vasculature in association with the rise in arterial pressure.
3. The dominant change seen after arterial pressure elevation has been maintained for 8 months is an increase in arterial wall mass, including an increase in vascular smooth muscle cell number, and in some arteries an increase in internal diameter.
4. It may be inferred from this limited study of elastic and muscular arteries that structural alteration represents the over-riding response of the vasculature to an elevation in intramural pressure.