Outer membrane proteins (OMP) isolated from four antigenically different strains of Hafnia alvei were tested for the toxicity, pyrogenicity, ability to induce Shwartzman reaction as well as for their influence on the leukocyte system. LD50 doses for the studied preparations determined on inbred mice were 18, 20, 28 and 34 mg/kg. These differences in the toxicity of the preparations were reflected in manifestation of Shwartzman reaction; more toxic preparations induced strongest necrohemorrhagic changes at the site of injection. The OMP preparations injected intravenously to rabbits caused moderate increase of body temperature. They induced changes in the number of leukocytes in the animals comparable with those of other preparates of bacterial origin.