Ganoderma lucidum is a well-known traditional Chinese medicine and often used for improving quality of life. Ganoderma lucidum polysaccharide (GLP) is the main active component in the fungus. Recent researches have shown that oral administration of GLP could produce immunomodulation and antitumor activity. With a high molecular weight, GLP is not easy to be absorbed, and the pathway via enteric mucosal immune response might be important for the immunomodulation of GLP. To investigate the potential mechanism, Kunming mice, weighing 20 +/- 2 g, were used and their peripheral blood mononuclear cells (PBMC), intraepithelial lymphocytes (IEL) and Peyer's patches lymphocytes (PPL) were separated, and incubated with GLP at different dosages (250 mu g/mL, 125 mu g/mL, 62.5 mu g/mL, 31.25 mu g/mL). MTT, ELISA and RT-PCR were used to detect the effects of GLP on the proliferation of the lymphocytes, and expression of IL-10, IL-2 and TNF-alpha. The results showed that GLP could stimulate the proliferation of PBMC and enteric mucosal lymphocytes, and promote the production of IL-2 and IL-10. The RT-PCR results also showed a higher expression of TNF-alpha and IL-10 mRNA in the lymphocytes. The higher expression of IL-2, IL-10 and TNF-alpha from the lymphocytes was observed at GLP concentrations of 62.5 mu g/mL and 125 mu g/mL. In conclusion, enteric mucosal immune responses could be one of the important pathways for the immunomodulation activity of GLP.