The results of the comparative toxicity studies of native lipopolysaccharide (LPS) of Rahnella aquatilis 96U037 and that modified by tin complexes indicates that, due to the modification of LPS by tin complex with benzoylhydrazone of 4-dimethylaminobenzaldehyde, a decrease of its toxicity was observed that led to disappearance of the pyrogenic effect. All obtained derivatives lost completely the antigenic activity both in homologous and heterologous systems which may indicate to the interaction of modifying complexes with certain groups being the components of antigenic determinant. The paper is presented in Ukrainian.