Heterospecific autoantibodies to axonal neurofilaments of neurons in sera from five patients with Creutzfeldt-Jakob disease were detected with the use of cryostat section from normal human brain caudate nucleus. The antibody, visualized by the indirect immunofluorescence technique, was shown to bind complement. This allowed to achieve brighter staining either by the anticomplementary method alone or by a combination of both anti-C3 and anti-IgG conjugates