An attempt to measure the distribution of blood in the functional kidney of dogs was made. The method involved the injection of liquid latex rubber into the vascular system at physiologic pressures, fixation of the rubber in situ, and then, after corroding away all tissue, measurement of the volume of the rubber casts. The kidney contains, in its functionally distended state, 14 per cent blood. Of this, 4.5 per cent is apparently in the arteries and some 7 per cent in the veins. The functional engorgement of the cortical interlobular veins (about 4 per cent) is particularly striking, for they form a dense palisade of 40 to 300 micro vessels. These are not seen at the usual autopsy since they have drained out and collapsed. It is pointed out that attempts to describe the blood distribution in the kidney after it has been drained of blood are of dubious value. In the light of these data, also, the nature of the measurement of "intrarenal pressure," accomplished by inserting a needle into the renal parenchyma, may be better understood: it is suggested to be primarily a measure of interlobular venous pressure.