Two new immunoelectrophoretic methods are described for studying the interaction of collagen fibrils with von Willebrand factor antigen (vWF: Ag). In the first, the sample was electrophoresed through a collagen-agarose wedge into an antibody-agarose area, and immunoprecipitin lines was detected by staining. Different immunoprecipitin patterns were obtained with the vWF: Ag of normal plasma, commercial FVIII preparations, and von Willebrand disease (vWD) type IIa plasma as the result of collagen binding of vWF: Ag. In the other method, the sample was electrophoresed into agarose for preliminary separation of forms, followed by migration in the second dimension through a collagen spacer gel into an antibody-agarose area. This method demonstrated preferential binding of high molecular weight forms of vWF: Ag in normal plasma and slight binding of the lower molecular weight forms of antigen found in vWD type IIa plasma. The affinity wedge method is a convenient general method for finding quickly a useful concentration of affinity reagent.