Abstract: | A method is described for the application of immunochemical stains to virus-infected cells in preparation for examination in the electron microscope. Specific antibodies to viral particles and to purified viral antigens have been rendered visible in the electron microscope by conjugation with the ironcontaining protein, ferritin. Examination of vaccinia-infected and influenza-infected cells treated with their specific ferritin-labelled antiserum has revealed the disposition of mature virus and viral precursors during various stages of the infection. Virus particles maturing at the cell surface and within the cytoplasm were specifically tagged and, in the case of influenza virus, the soluble, nucleoprotein viral-precursor was identified in distinct portions of the nucleus. |