Cryoprecipitated factor VIII/von Willebrand factor (FVIII/vWF), freed of fibrinogen by clotting with calcium and Defibrase®, was chromatographed on Sepharose CL-2B. Fractions containing lower-molecular-weight forms of FVIII/vWF comprised coprecipitated plasma proteins of similar molecular weights. The major contaminants, fibronectin and IgM, were removed by affinity chromatography on gelatin- and anti-IgM-agarose, respectively. Finally, pure low-molecular-weight FVIII/vWF protein was harvested in the void volume fraction of a Sepharose CL-6B column. The smallest multimers had the size of the tetramer of the basic subunit chain of FVIII/vWF