A lipopolysaccharide from wheat flour (LPSw) which was isolated and characterized is shown to exert definitely a suppressive effect on incidence of type 1 diabetes in mice. Therapeutic effect on type 2 diabetes in patients was also obtained, though only from preliminary results. The percutaneous route of administration is most favorable. The important role that precursor tumor necrosis factor, free or cell bound, may play in this mechanism is discussed.