Purified vaccinia virus freed from demonstrable hemagglutinating activity was inactivated and, subsequently, disintegrated by treatment with pepsin. The preparations obtained were examined in the electron microscope and tested for hemagglutinating and precipitating activity as well as for their immunogenicity. The release of hemagglutinating activity from the virions was dependent upon the concentration of pepsin used. Precipitinogens and antigen capable of inducing complement fixing antibodies in rabbits were released by low concentrations of pepsin. Formation of neutralizing and especially hemagglutination inhibiting antibodies was induced by preparations obtained by treatment with higher concentrations of pepsin. Immunization with one mg, but not with 0.1 mg, of inactivated but undigested virions resulted in formation of hemagglutination inhibiting antibodies. The site of a hemagglutinin component in the vaccinia virion is discussed.