A simple perfusion apparatus modified from procedures used and published in renal studies is presented and discussed. The buffer and fixative solutions to be perfused are placed in closed reservoirs under 20 mm of Hg pressure which is provided by a constant inflow of air from an air inflow valve present in any routine laboratory. The pressure is monitored by a sphygmomanometer gauge and adjusted with an air control valve. The perfusate solutions are kept at 37 degrees C. The oncotic-osmotic characteristics of routine buffer and fixative perfusates are presented and discussed. The perfusion technique utilized in a cat model is detailed. The technique does not require sophisticated equipment and yet perfusion conditions can be carefully monitored and controlled.