A new type II variant form of von Willebrand's disease has been recognized in a mother and daughter who have bleeding manifestations typical of von Willebrand's disease. Laboratory findings include consistently prolonged bleeding times, with normal levels of factor VIII procoagulant and antigen, but decreased ristocetin cofactor activity. Electrophoresis in SDS 1.5% agarose gel and reaction with 125I-labeled anti-factor VIII-related antigen rabbit IgG, followed by autoradiography, revealed that both plasma and platelets lack the large multimers of factor VIII-related antigen. In 2.5% gel, the propositus plasma lacked the normal “triplet” pattern. In 3.0% gel, a 5-band pattern was observed in normal, type IIA, and type IIB plasma, whereas type IIC plasma revealed a 2-band pattern. The patient's plasma revealed a 4-band pattern distinctly different from normal or other type II variants. We suggest that this new variant be labeled type IID, until a more appropriate nomenclature is developed.