Pinealectomy in the rat induces a significant increase of the arterial blood pressure within 15 days from the surgical procedure; this hypertension is still present 30 and 60 days after pinealectomy while after 90 days it returns to the normal range. Histological examination of the kidneys of pinealectomized hypertensive rats shows wall thickening and lumen narrowing of the arterioles, adventitial and periadventitial fibrosis, dense glomeruli. The vascular lesions are not diffuse but patchily distributed. Body weight is higher in pinealectomized rats compared with normal and sham-operated animals: this difference becomes significant about 40 days after pinealectomy and gradually decreases until it disappears at the end of the third month. Food and water intake is higher in pinealectomized rats up to the 7th week; during the 8th week they return to the normal range.