In this study a search for F. tularensis antiphagocytic factor and an attempt for its isolation were made. For this purpose a fraction of F.tularensis water-saline extract saturated 55-60% with ammonium sulfate was split into separate components by preparative methods. One of them, consisting of two antigens of glycoprotein nature, had the capacity of decreasing the digestion of F.tularensis by guinea pig peritoneal macrophages about 10 times. The study revealed that the protein of the preparation obtained in this investigation was capable of suppressing digestion, thus facilitating the active proliferation of F.tularensis inside the cells of the host body.