Pathological findings and rickettsia on rodent-lung are increased after inoculation into rodent which had been injected by CORTISONE used 0.3-0.4 mg per 10g of body-weight as dosis. H-antigen prepared from emulsion of lung which appeared severe pathological findings shows antigenic nature specifically as positive floculation. test for antibodies produced by Rickettsia orientalis as follows: 1. F-antigen fraction which are fresh emulsion of infected lung do not appear positive floculation against homologous antibodies produced by Rickettsia orientalis. 2. But the F-antigen appears positive reaction after the manipulation of which the material contains F-antigen fraction are frozen and disolved quickly 2-3 times continuously by dryice-Acetone. 3. H-antigen shows positive reaction against homologous antibodies whether the emulsion contains Rickettsia or not. 4. The positive serological reaction as floculation test between H-antigen and homologous antibodies appears rapidly within 4.5 minutes.