Our previous studies have demonstrated that glucan isolated from Saccharomyces cerevisiae is a unique reticuloendothelial (RE) agent and induces a profound enhancement in humoral and cell-mediated immunity. Relative to the anti-tumor effect of glucan, glucan administration is associated with inhibition of tumor growth, and regression as well as an enhancement in survival of mice and rats when challenged with various tumor models. Since we have previously reported that specific water soluble di and oligosaccharides of glucan have RE stimulating activity, efforts will be made to develop water soluble tumor inhibitory fractions of yeast glucan. The proposed research provides for 1) the continued development of glucan as an immunostimulant, 2) the assessment of the mechanism of action of particulate and soluble glucan, 3) the interrelationships between glucan immunotherapy and chemotherapy, and 4) the assessment of the ability of glucan to modify tumor induced anergy as well as bacterial, viral and fungal infections in control and tumor-bearing mice. It is apparent from the composite experimental and clinical data obtained to date that water soluble glucan derivatives offer significant potential in immunotherapy as well as immunoprophylaxis.