The White-type polysaccharide (WPS), often called Freeman polysaccharide, was obtained by hydrolyzing gram-negative bacteria in 0.2 N acetic acid at 100 degrees C for 2 h. The crude product contained partially degraded O-antigens as well as other components that were active as immune adjuvants, enhancers of macrophage cytotoxicity of tumor target cells, and inducers of osteoclastic bone resorption. The same WPS preparation augmented the tumor cytotoxicity of normal mouse spleen cells and slightly retarded the take of L1210 leukemia in mice. The WPS preparations generated colony-stimulating factor in mice but were not active in lymphoproliferative (mitogenicity) tests. Chemical analyses of the WPS preparations did not detect the presence of components characteristic of the lipid moiety of endotoxins. The WPS samples were also negative in biological assays of endotoxicity such as local Shwartzman and toxicity tests. These findings indicate that gram-negative bacteria contain nonendotoxin components that are potent modifiers of some biological responses.