The authors examined a total of 11 lower extremities in 10 patients with chronic occlusion of the superficial femoral artery (mean length of occlusion 17.2 cm) in order to compare the participation of the heterocollateral and homocollateral circulation in the maintenance of the ankle pressures assessed by the Doppler principle. Before percutaneous transluminal recanalization of the chronic occlusion of the superficial femoral artery the authors induced by means of a balloon catheter short-term occlusion of the deep femoral artery in its central portion, closely after its insertion (complete block of the heterocollateral circulation) and in the periphery of this artery (partial block of the collateral circulation). During both types of balloon occlusion the authors assessed the ankle pressures and compared them with control values, assessed before occlusion. The authors found that in their patients the heterocollateral circulation, as compared with the homocollateral one, participated substantially more in the value of the ankle pressure at rest. The importance of the heterocollateral circulation increased with the length of chronic occlusion of the superficial femoral artery. In some patients the homocollateral circulation did not participate at all in the maintenance of the ankle pressure. A drop of the ankle pressure in patients with chronic occlusion of the superficial femoral artery is also more marked in acute occlusion of the deep femoral artery in its central portion, as compared with acute occlusion in the periphery.