A new electrophoretic method is described for rapid screening of abnormalities of the multimeric structure of von Willebrand factor in von Willebrand's disease. The method is based on the transfer of the separated proteins from agarose gels onto nitrocellulose foils followed by immunoperoxidase staining. It has the advantage of not requiring radio-iodinated antibodies and reduces the working time for the entire procedure from 5-6 days to 3 days. Electroblotting followed by immunoperoxidase staining differentiates patients with intact multimeric structure from those without intermediate and/or large multimers. The more subtle defects of the inner structure of the smallest multimers found in patients with type II von Willebrand's disease can also be identified. A potential disadvantage of electroblotting and immunoperoxidase staining is the lesser sensitivity of this technique, which results in the detection of a smaller number of multimers (11-12 bands) than by autoradiography without transfer onto nitrocellulose (16-17 bands).