Modulating effects of Candida albicans on the immune responses of mice immunized with sheep red blood cells(SRBC) were assessed both by footpad tests for anaphylactic, Arthus and delayed type hypersensitivity rections against homologous and heterologous antigenic challenges and by serum antibody titrations for hemagglutinin and hemolysin against SRBC. The results are summarized as follows: 1. In the mice simultaneously immunzed with C. albicans and SRBC, anaphylactic type and Arthus type footpad reactions to C. albicans challenge were enhanced, and extents of the enhancements were proportional to the concentration of SRBC administered for immunization, reaching peak in mice immunized with 0.2ml($10^8$) of 5% SRBC suspension. Although a little enhancement of delayed type hypersensitivity to C. albicans was observed in those mice, there was no significant difference between the mice groups immunized either with SRBC alone or SRBC and C. albicans simultaneously. 2. Simultaneous immunization of mice with C. albicans and SRBC resulted in the suppression of both anaphylactic type and Arthus type footpad reactions to SRBC, and the extent of such suppressions was inversly proportional to the numbers of C. albicans administered for immunization. Delayed type reaction of the mice to SRBC varied little in regards to the different numbers of C. albicans injected. 3. Hemagglutinin titers differed little between the mice groups immunized with SRBC alone or with SRBC and C. albicans simultaneously. Hewever, hemolysin titers were lower in the mice immunized simultaneously with SRBC and C. albicans. 4. In the peripheral blood of mice immunized simultaneously with SRBC and C. albicnas. there observed increases in the percents of monocyte and polymorphonuclear leukocytes and decrease in the numbers of lymphocytes and pyroninophilic lymphocytes. These results indicated that C. albicans is an immunosuppressant of the mice to SRBC when both anteigns were administered simultaneously for immunization, and that SRBC acted as an enhancer of anaphylactic type and Arthus type reaction of mice to C. albicans when administered simultaneously.