In a retrospective study of 217 patients, smoking habits were related to the late patency rates of arterial reconstructions performed for ischaemia of the legs. Patients who had stopped smoking or who smoked no more than 5 cigarettes per day after the operation had late patency rates of approximately 90 per cent for aortofemoral reconstructions and 80 per cent for femoropopliteal vein grafts. Patients who continued to smoke more than 5 cigarettes per day were approximately three times more likely to block an aortofemoral reconstruction and four times more likely to block a femoropopliteal vein graft. The results were similar for males and females, for various age groups, for claudicants and patients with severe ischaemia and for aortofemoral endarterectomy and Dacron grafts. The late patency rate was approximately inversely proportional to the number of cigarettes smoked per day after the operation. There was no such correlation with the number smoked per day before the operation.