The purpose of this study was to compare the conduct and early results of infrainguinal vascular reconstructions with use of ancrod or heparin for anticoagulation.To test the hypothesis that ancrod was an effective alternative to heparin, 28 patients requiring infrainguinal bypass surgery were randomized to receive heparin during operation or ancrod before operation over a period of 12 hours to deplete circulating fibrinogen (0.2 to 0.5 gm/L).No clotting of blood within the grafts or native vessels was noted during the conduct of the surgical procedures in either group. No excessive bleeding was detected during operation in either group. The operative procedure, complication rate, and hospital course were also indistinguishable; patency at 1 month was also equal.Fibrinogen depletion with ancrod provides anticoagulation for the conduct of infrainguinal vascular reconstructions that is as effective as heparin. When heparin is contraindicated ancrod is an effective and safe alternative.