Adsorption states of influenza virus, Lee strain, on chicken red cells were studied under electron microscope. Treating electronmicrographs quantitatively, adsorption end point was determined. From this end point, that the foundamental idea of CCA titration by Miller and Stanley had been fare, was proved. From some pictures, it was concluded that owing to agglutination of virus particles by antisera, the red cell agglutination inhibiton reaction would be caused. And virus particles adsorbed on chicken red cells were inversely eluted and agglutinated when anti-viral serum added after complete adsorption. This latter phenomenon was named as “robbing off reaction” by antisera.