The immunomodulating effect of a new polysaccharide-peptide complex from culture mycelia of Lentinus edodes (LE) was studied for elucidation of the mechanism of augmentation of cell-mediated immunity. RNA samples were isolated from the untreated and treated murine splenocytes and human peripheral blood mononuclear cells. RT-PCR was used to analyze the cytokine gene expression and bioassay was used to analyze the cytokine production. By administration of LE, the expression levels of IL-2 and TNF-alpha genes were augmented in the treated murine spleen mononuclear cells and human peripheral blood mononuclear cells. The production of IL-2 were augmented in the treated murine spleen mononuclear cells, and the production of TNF-alpha were augmented in the treated murine peritoneal exudate macrophages. The production of IL-2 and TNF-alpha were augmented in the treated human peripheral blood mononuclear cells. These results suggest that LE may induce Th immune responses.