This study was carried out to assess the efficacy of NHS 8Y concentrate in the treatment of patients with von Willebrand's disease (vWD). Eight patients (two type I vWD, one type IIA vWD, two type IIB vWD, and three type III vWD) were treated on a total of 10 occasions with 8Y. Following each treatment episode there was a temporary correction of patients' bleeding time (BT) measurements. Other laboratory parameters--von Willebrand factor ristocetin cofactor activity (vWf:RiCo), vWf antigen (vWf:Ag) levels, and factor VIII coagulant activity (factor VIII:C)--were also corrected. Plasma vWf multimers temporarily reflected those present in the infused concentrate. An effective clinical response was observed in each case despite, as revealed by autoradiography and scanning densitometry of SDS-agarose electrophoresis gels, a reduction in the concentration of the largest vWf multimers in 8Y compared with normal plasma. Overall, the clinical effectiveness of 8Y in vWD was comparable to that seen with cryoprecipitate. We conclude that NHS 8Y concentrate may be used as an alternative to cryoprecipitate for the treatment of vWD.