A new and simple procedure for producing experimental hypertension in rats is described. It consists in the complete ligature of the aorta between the origin of the renal arteries. Production of an atrophic left kidney depends closely on the rat's body weight, occurring in about 90% of rats weighing over 300 g and almost never in those weighing under 150 g. The great majority of rats weighing more than 300 g with atrophic left kidneys were hypertensive.