Effect of antiplatelet and anticoagulant therapy on patency of femorotibial bypass grafts. In a retrospective study, 210 autogenous femorotibial saphenous vein grafts inserted during the 15 years from 1967 to 1982 were followed-up for a mean period of 62.3 +/- 5.7 months. Seven patients, who had had eight grafts died in hospital. The remaining 202 grafts fell into three groups: (1) Sixty grafts in patients who received 325 mg of dipyridamole and 1.0 g of acetylsalicylic acid daily, starting on the second postoperative day and continuing for six months. (2) One hundred and two grafts in patients on no antithrombotic therapy. (3) Forty grafts in patients on warfarin therapy to maintain the prothrombin time (prothrombin-proconvertin method) within the therapeutic range (0.10 to 0.20). Medication was continued for six months. This group included more high-risk patients than the other two groups. The mean ages and the incidence of risk factors did not vary significantly between the groups. The patency rates in three groups at five years were 62.5%, 44.0% and 26.0% and at ten years 48.5%, 25.0% and 21.5% for the dipyridamole and acetylsalicylic acid, no therapy and warfarin groups, respectively. The limb salvage rates were 100%, 96% and 85% in the dipyridamole and acetylsalicylic acid, no therapy and warfarin groups respectively. Thus, the best results were seen in the aspirin/dipyridamole group. 