Many cytokines, in particular tumor necrosis factor (TNF)-alpha have been known to play an important role in the pathogenesis of gastric mucosal lesions caused by various factors such as drugs and Helicobacter pylori infection. Our previous studies have shown that the polysaccharide fractions isolated from the fruiting bodies of Ganoderma lucidum (GLPS) prevented indomethacin- and acetic acid-induced gastric mucosal lesions in the rat. However, the mechanisms remain unclear. This study aimed to investigate whether GLPS had a direct mucosal healing effect in the indomethacin-treated rat, and to explore the possible mechanisms by determining the gastric mucosal mRNA and protein levels of TNF-alpha and ornithine decarboxylase (ODC) activity. In addition, the effects of GLPS on the cellular proliferation, ODC and c-Myc protein expression and mucus synthesis in the rat gastric cell culture (RGM-1) were examined. The present study demonstrated that GLPS at 250 and 500 mg/kg by intragastric input caused ulcer-healing effect in the rat; this was accompanied with a significant suppression of TNF-alpha gene expression, but with an increased ODC activity. In RGM-1 cells, GLPS at 0.05, 0.25 and 1.0 mg/ml significantly enhanced [3H]thymidine incorporation and ODC activity in a concentration-dependent manner. However, these effects were abrogated by the addition of the ODC inhibitor, DL-alpha-difluoromethyl-ornithine (DFMO). GLPS at 0.25-1.0 mg/ml also increased mucus synthesis, as indicated by the increased D-[6-3H]glucosamine incorporation in RGM-1 cells. Furthermore, GLPS at 0.05-1.0 mg/ml increased the c-Myc protein expression. These findings indicated that GLPS produced a mucosal healing effect in the rat model, perhaps due partly to the suppression of TNF-alpha and induction of c-myc and ODC gene.