A method for assessment of arterial collateral vessels and corresponding stenoses on arteriograms of arteriosclerotic legs is presented. The method is based on the concept that compensatory collateral vessels, by-passing stenoses of the conductive arterial segments, have to cross a plane traversing the distal part of each segment (common iliac artery, external iliac/common femoral artery and superficial femoral artery). The number of collateral vessels was counted and the minimum diameter within the corresponding conductive arterial segment was measured (three locations in each leg). There was a close correlation between the sum of remaining lumen diameters and the sum of corresponding collaterals in thirty-four legs (r = -0.77, P less than 0.001). Maximum lower leg blood flow during exercise (thermodilution) was better correlated to arteriosclerotic changes in the pelvic arterial tree than to changes in the femoral arteries, and the must abundant collateral vessels were found in individuals having central stenoses or occlusions.