Abstract
A new technique for the electron microscope localization of bacterial surface antigens, using unlabeled antisera, has been developed. This technique, called the "immuno-coating reaction" was applied to serological studies of Streptococcus sanguis, using antisera which had been shown to be specific for this species by gel diffusion analysis. The results of the immuno-coating reaction confirmed the specificity of the antisera for S. sanguis. In addition, the data indicate that some of the antigens responsible for the reaction were proteins which formed filamentous processes on the surface of the cell.