The nature of sugar chain of factor VIII related protein (VIIIR) in the plasma of normal subject and patients with type I and IIA of von Willebrand's disease was examined by crossed affinoimmunoelectrophoresis using anti-human factor VIII rabbit serum, with inserted wheat germ agglutinin (WGA) agarose layer. Molecular weight disfribution and affinity for WGA of factor VIII related antigen (VIIIR: AG) were estimated by the electrophoretic patterns.VIIIR: AG, in normal plasma and in type I of von Willebrand's disease, showed high affinity for WGA at the portion over 3×106 daltons of molecular weight. On the other hand, VIIIR: AG in plasma of type IIA consists only of the multimers smaller than 3×106 daltons, showing a very weak affinity for WGA.These results suggested that VIIIR-multimers in type IIA may be poor in sialic acid reactive with WGA, in addition to incomplete polymerization.