A patient with von Willebrand's disease underwent cholecystectomy after replacement therapy with a factor VIII concentrate that had been sterilized by treatment with tri(n-butyl)phosphate and Tween 80. The patient received 53 units of factor VIII per kg of body weight prior to operation. In addition, a total of 280 units of factor VIII per kg was infused within 10 days after operation. This replacement regimen prevented excessive bleeding during surgery and supported normal hemostasis during the postoperative period. Analysis of the multimeric pattern and the functional assay of von Willebrand factor in factor VIII concentrates indicated that the procedures utilized for virus inactivation had no significant deleterious effect upon the quality of von Willebrand factor molecules.