A simple infusion system to assess the status of distal runoff was investigated on both hindlimbs of five mongrel dogs. Infusion catheters were placed in the superficial femoral arteries and the origin of the lower leg arteries was exposed for anatomic manipulation of the distal runoff. Saline solution was infused through the superficial femoral arteries at 64, 129, and 193 cm levels to calculate volume flow and index of resistance to flow. The in vitro part of the study was undertaken to analyze the effect of different-size catheters on flow rates in a rigid undistensible model. In the hindlimb study the flow differed significantly between two- and one-vessel runoff status at 50 and 100 mm Hg infusion pressures. In the in vitro study, in contrast to the hindlimb study, index of resistance to flow values for different-size catheters remained almost unchanged as the infusion pressure increased, demonstrating the distensibility of the runoff bed in dogs. A preliminary clinical study in 13 patients undergoing infrainguinal bypass surgery demonstrated a good correlation between angiographic runoff evaluation and intraoperative flow values. Valuable information can be obtained about the status of the distal runoff by this simple infusion method, which might be used to improve the prediction of outcome of infrainguinal bypass surgery.