A M(r) 110,000 glycoprotein, designated gp110, isolated from the concanavalin A-Sepharose-binding protein fraction of the chemically induced BALB/c Meth A sarcoma by Mono Q fast protein liquid chromatography, has been shown to: (a) increase the resistance of these mice to growth of the Meth A sarcoma, but not the antigenically unrelated BALB/c CI-4 sarcoma, and (b) induce an antitumor cellular immune response in mice, which was detectable in cell-mediated cytotoxic assays. The immunogenicity of the concanavalin A-Sepharose-binding protein fraction of Meth A cytosol had been attributed to gp96, the major component of this fraction. The evidence presented here, however, demonstrates that Meth A gp96, when sufficiently purified, is nonimmunogenic. The results of the present analysis of gp110 strongly support the concept that gp110 represents a family of proteins expressed on a variety of chemically induced tumors, in which variations in molecular fine structure account for the antigenic diversity associated with these tumors.