A dietary supplement containing an extract of the Basidiomycete fungus Agaricus blazei Murill with potential chemopreventive, antineoplastic and immunopotentiating activities. Agaricus blazei Murill extract contains high levels of phytochemicals, especially beta-D-glucans. Beta-D-glucans may promote dendritic cell (DC) maturation; increase interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha) and immunoglobulin levels; and may enhance natural killer (NK) cell activity, potentially boosting anti-tumor host immune responses.