Bovine sera for tissue culture use were shown to contain heterophil antigen of the Paul-Bunnell-Davidsohn type by immune adherence hemagglutination tests with sera from patients with infectious mononucleosis. The antibody titers observed were comparable to those determined by two other methods; i.e., the immune adherence hemagglutination test was found to be as specific as the differential absorption test with horse erythrocytes or the ox cell hemolysis assay, but it appeared to be the most sensitive of the three procedures. All 16 individual or pooled bovine serum samples showed Paul-Bunnell-Davidsohn antigen at concentrations varying over a fourfold range. The potential usefulness of the immune adherence hemagglutination test for various Paul-Bunnell-Davidsohn antigen-related problems and implications of the observations are discussed.

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