1. The rabbits of a commercial stock were immunized by the intravenous inoculation of live Cryptococcus neoformans of the Ishino strain at the concentration of 1 mg per cc. The antigen was injected thrice a week for 3 consecutive weeks. The immune serum with the agglutination titer of 1:1, 024 against the homologous organism was obtained 5 weeks after the last inoculation.
2. The tube agglutination test with this immune serum gave the following agglutination titers, 1:128 against Cryptococcus neoformans (C2-4 strain), 1:32 against Cryptococcus diffluens and 1:8 against Torulopsis sake and Torulopsis pinus, respectively.
3. The slide agglutination test showed that the differentiation between Cryptococcus species and Torulopsis species was made if the antiserum was diluted to 1:10.
4. The γ-globulin concentation of the fluorescein isothiocyanate-labeled antibody solution was 0.52% which was completely able to differentiate between Torulopsis pinus and Cryptococcus species if diluted to 1:8. The fluorescent antibody technic was able to afford us making a diagnosis without difficulty when the fluorescein isothiocyanate-labeled antibody was prepared from the immune serum with agglutination titer as high as possible and diluting it to some extent. (In the author's experiment, diluting to 0.0165% of γ-globulin was most effective.)