Seventy-one patients underwent a classical reversed saphenous vein graft for femoropopliteal occlusive disease and were enrolled in a controlled clinical trial. During the second postoperative week the patients were allocated randomly into one of two groups; group 1 consisted of 34 patients who received coumarin, group 2 (37 patients) served as a control group without any anticoagulant treatment. The mean follow-up was 18 months. After 12 months the cumulative patency rate was 81 per cent and after 18 months 75 per cent; for patients receiving coumarin treatment, the respective figures were 90 and 82 per cent and for those with no anticoagulant treatment 72 and 67 per cent, the decrease being significant. When the bypass operation was performed for limb salvage (clinical stages III and IV) the overall results were worse (12 months, 72 per cent; 18 months, 68 per cent) than in stage II and stage II-III (12 months, 90 per cent; 18 months, 85 per cent). In limb salvage surgery the positive effects of anticoagulant treatment were significant (with treatment: 12 months, 87 per cent; 18 months, 87 per cent; without treatment: 12 months, 60 per cent; 18 months, 53 per cent). The site of the distal anastomosis (above knee: 12 months, 81 per cent; 18 months, 73 per cent versus below knee: 12 months, 80 per cent; 18 months, 75 per cent) did not have any demonstrable influence on the patency rate.