The use of the agar gel diffusion technique has established the presence of three distinct antigenic reactions in the sera of Ad. 12 tumor-bearing hamsters. Only one of these antigens is directly demonstrable in the tumor. This "tumor" antigen is also formed during early stages of the infectious cycle in tissue culture cells. Other antigens present in the tumor, but only demonstrable indirectly with the use of antibody-containing serum of tumored hamsters, are the classical type-specific C antigen, and a new antigen, termed D.
Of ninety-eight Ad. 12 tumored hamster sera, six reacted in gel diffusion with virus and tumor preparations, and thirty-one with tumor only.
Sera which reacted in gel diffusion with viral antigen uniformly bad neutralizing antibody and high titers of CF antibody against viral and tumor antigens; however, many sera with comparable antibody titers did not react with the virus in gel diffusion. Sera which reacted in gel diffusion only with tumor antigen also had high CF antibody titers, but there was no correlation with neutralizing antibody.