This study was designed to evaluate the antitumor activity of CSBG, purified from the cell wall of Candida albicans IFO1385. First, as an effect of CSBG on P815 mastocytoma, significant prolonged survival and suppression of the tumor growth were observed. Second, the transfer of spleen cells from CSBG-sensitized BALB/c mice to CDF1 mice led to further suppression of tumor growth as well as P815-immunized spleen cells. Third, CSBG enhanced antitumor immunity in gene therapy using B7-1-transfected P815 cells. These results strongly suggest that CSBG enhances the host defense response to tumor due in part to an adjuvant effect.