To estimate structural changes in the kidneys exposed to chronic venous congestion, a 65-75% stricture was made in the pulmonary trunk of 24 pups. Twelve dogs were controls. The animals were followed up from 6 months to 2 years. Venous pressure was measured, the kidneys were studied histologically, stereometrically and morphometrically. There was hypertension in the posterior vena cava reflecting chronic defects in the venous blood outflow from the kidneys. The capacity of the venous and arterial renal circulation was increased and reduced, respectively. There was some reduction of the glomerular system. Muscular hypertrophy of the walls of renal veins and arteries was adaptive. Pathological alterations in the kidneys were represented by sclerosis of the walls of the renal veins, connective tissue thickening of arterial intima, sclerosis and hyalinosis of arterioles and glomeruli, dystrophy of canalicular epithelium, renal parenchyma atrophy, renal stroma growth.