Most of our knowledge concerning the blood flow through the glomerulus and, in general, the microcirculation of the kidney has been derived from studies using primarily the frog kidney. A technique is now available whereby one can study the living mammalian renal circulation. This preparation consists of transplanting renal tissue into a chamber in the cheek pouch of the hamster. After approximately two days full circulation through the transplant is established and one can readily discern circulation through the afferent arterioles, glomeruli, vasa rectae, etc. It is proposed to use this preparation to obtain new information concerning the microcirculation of the mammalian kidney with particular reference to the study of the site of action of drugs, the influence of altering intravascular volume and the influence on this homograft of inducing hypertension in the recipient.