The differences in pathology of the leg and foot arteries are described in patients with thromboangiitis obliterans (60 cases) and atherosclerosis (30 cases). Based on the operative and biopsy material it has been shown that thromboangiitis obliterans is associated with immune inflammation of the arteries, manifesting itself by productive or, more rarely, by necrotic arteritis. In the latter condition, the wall of the impaired vessels contains immune complexes. In patients with atherosclerosis, the muscular type arteries of the legs and feet show dystrophic and fibroblastic lesions seen primarily in the intima and manifesting themselves by the enlargement of its connective tissue. No immune complexes were discovered in the wall of such arteries.