1. Structural changes in the thymus during the evolution of experimental renal hypertension were investigated to determine their possible role in the genesis of hypertensive vascular disease.
2. The thymus, adrenal glands and the progression of hypertensive vascular lesions were investigated in rats during the first 30 days after occlusion of the aorta between the two renal arteries.
3. Hypertension was initially accompanied by marked atrophy of the thymus, most pronounced 9 days after operation. During this time, the adrenal glands doubled in size and the heart became enlarged.
4. After 21 days the thymus regenerated and became hypertrophic. Histological features of hyperactivity accompanied by infiltration of plasma cells were evident, while the adrenal glands remained enlarged.
5. The observed structural changes of the regenerated thymus in the presence of sustained adrenal hypertrophy indicate that the thymus may contribute to the production of hypertensive vascular disease.