By the perfusion method through the kidney of the toad following results were obtained. 1) When the Extr. of Rad. Phytol. is added to the perfusing fluid, it increases distinctly the flow of urine. 2) Conversely, the addition of potassium salt, which will be contained abundantly in Rad. Phytol., brings, firstly, the remarkable decrease of the urine flow, and then it may increase slightly. 3) Ash of the Rad. Phytol. dissolved in Ringer's solution decreases the urine flow remarkably at first, and then it may increase. 4) When the Extr. of Rad. Phytol. is applied in drops to the exposed kidney of frog, causes dilatation of glomerular capillaries; the circulation in them becomes more rapid, i.e. the quantity of blood which flows through them increases, and a number of glomeruli, hitherto invisible, becomes visible. The application of this extract in drops on the web of frog dilates its blood-capillaries and increases the blood-flows through them. 5) But the solution of potassium salt used, or the ash of the Rad. Phytol. causes contraction of glomerular capillaries and capillaries of web of frog. The blood-flows in the capillaries become remarkably slow, i.e. the quantity of blood which flows through them decreases. The glomeruli, hitherto activ, becomes stationary and visible number of glomeruli diminishes. 6) The measurement of the freezing-point revealed that the osmotic pressure of the Extr. of Rad. Phytol. used was not very different from the normal Ringer's solution. 7) By the flame-reaction it was ascertained that potassium and sodium salts were contained in the Rad. Phytol. 8) Diuretic action of Rad. Phytol. is due to some organic substance, which causes dilatation of capillaries of glomerulus and web of frog. Potassium salt which is contained in Rad. Phytol. makes some additional action through hydraemia.