Tiprotimod is a new synthetic thiazole derivative of cefodizime. It is an immunopotentiator of low molecular weight. The broadest immunological activity was seen for this drug. The drug was able to enhance the delayed type hypersensitivity-response against sheep erythrocytes (SRBC) and to stimulate the humoral immune response against Tetanus toxoid and heat-killed E. coli. In the popliteal lymph node assay, a murine graft-vs-host model, a stimulating effect of the substance was observed when it was administered at the same time of the grafts to rats. These results demonstrate that tiprotimod is a potent immunopotentiator for both humoral and cell mediated immune response in experimental animals. The ability of the tiprotimod molecule to enhance the production of ROS by stimulated polymorphonuclear leukocytes and to act agonistically with TNF-alpha or lipopolysaccharide is abrogated when tiprotimod is part of the cefodizime molecule.