1. The rabbits of a commerical stock were immunized by the technique of thermostable antigen with Candida albicans of IFO 0583 strain. The agglutination titer of the immune serum was 1:5120 against the hemologous organism. 2. The antiserum of rabbits was labeled with the fluolescein isothiocyanate. The agglutination titer of the labeled antisterum was 1:160 against Candidd albicans (the homologous organism) as well as Torulopsis famata of normal flora in the rat-stomach. The common determinants of the two strains were also identified by the precipitation reaction. 3. The mono specific antiserum was obtained by absorbing the above mentioned labeled serum with Torulopsis famata. The thus absorbed labeled antiserum showed the agglutination-titer 1:5 against Candida albicans and no titer against Torulopsis famata, whereas the band of precipitate in the Ouchterlony method was found against only Canaida albicans. The gamma globulin concentration of the fluorescein isothiocyanate-labeled, absorbed and mono specific antiserum solution was 0.9mg/ml. 4. Fungi in the gastric ulcers of human and rats could be identified as Candida albicdns by its specific fluorescence when stained with the fluorescein isothiocyanate-labeled, absorbed and mono-specific antiserum.