Occlusion of the left subclavian artery was demonstrated following exposure to two courses of radiation, the patient having received 4,200 rads in 4 weeks 9 years previously, and 4,000 rads in 8 weeks almost 5 years previously. Despite other intercurrent medical conditions, this seems to be a cause-and-effect relationship, since the only segment of abnormal artery was confined to the limited volume receiving the double exposure, whereas other arteries nearby did not demonstrate abnormality.