THE NUMBER of patients with slowly progressive thrombosis of the abdominal aorta has been small. In a review of the literature, Greenfield,1 in 1943, stated that 161 cases of thrombosis and embolism had been reported. In 1940 Leriche2 presented an excellent summary of the clinical course of progressive thrombosis of the abdominal aorta. On 4 patients he performed a bilateral lumbar sympathectomy, and in 1 patient he excised the lower portion of the abdominal aorta, removed the left lumbar chain and sectioned the right chain below the third lumbar ganglion. Two patients were recently treated by me, and their cases are being presented in this paper. These cases are to be sharply differentiated from cases of acute embolic obstruction and rapidly progressive thrombosis of the aorta. The development of the clinical syndrome into a recognizable pattern occurred over the course of three months. In both patients, a collateral