In five female pigs, weighing approximately 100 kg, laparotomy was made under surgical anesthesia. One kidney was removed for immersion fixation and enzyme histochemistry, while the other kidney was fixed by vascular perfusion without prior interruption of the blood flow. A step-by-step description is given of the perfusion procedure, which requires three assistants. Prior to perfusion, heparin was given in order to prevent intravascular coagulation. 1% glutaraldehyde in Tyrode’s solution was used as perfusion fluid. Polyvinylpyrrolidone 2.5% was added in order to adjust the colloid osmotic pressure of the perfusion fluid to that of the blood. Perfusion was maintained for 5 min. The tubules appeared with open lumina, and the proximal tubular cells had evenly arranged brush borders and both lateral and intercellular spaces were narrow and of constant widt