Diagnosis of von Willebrand's disease

31 patients with the diagnosis or presumed diagnosis of von Willebrand's disease were reinvestigated by means of Ristocetin cofactor-activity and factor VIII-associated antigen. In addition a family with a variant of von Willebrand's disease is described. Ristocetin cofactor-activity was found the most reliable test, its value for the diagnosis of mild forms and of variants of von Willebrand's disease is further established by these results.