Perinephritic hypertension was induced in mongrel dogs by cellophane encapsulation of one kidney and simultaneous contralateral nephrectomy. Systolic blood pressure began to rise before diastolic blood pressure and both reached maximal values 3 weeks after surgery, their levels becoming stable thereafter up to the end of the study (20 weeks). Cardiac contractility, measured by the index dp/dt/P<sub>40</sub> (rate of rise of isovolumic left intraventricular pressure at a developed left ventricular pressure of 40 mm Hg) was not altered during the evolution of hypertension; heart weight and left ventricular thickness were increased. Plasma renin activity markedly decreased in the chronic phase and plasma urea and creatinine levels rised initially in a moderate but significant way, thereafter remaining stable. The structure of the wrapped kidney remained normal 20 weeks after surgery, when microscopic arterial lesions were seen in other organs. The comparison of the evolution of this hypertensive model with other more commonly used renal experimental hypertension types allows us to conclude that cellophane perinephritic hypertension in the dog must be considered as an individual entity.