Abstract.The multimeric structure of von Willebrand factor (vWF) and its ristocetin‐induced binding to platelets, using a simple and very sensitive radiomonoclonal antibody‐labeled vWF method, was compared in normal plasma, single‐donor cryoprecipitate (CP) and five different antihemophilic factor (AHF) concentrates. All the AHF showed a lack of larger vWF multimers, an abnormal ‘triplet’ pattern, and much lower vWF binding to platelets than that of plasma or CP, vWF being the lowest for those with a lesser proportion of larger vWF multimers. These results suggest that the combination of vWF multimeric analysis and the radiomonoclonal‐labeled vWF method may be very useful in the assessment of AHF p