Previous investigations have shown that interleukin-11 (IL-11) and the IL-11 receptor (IL-11R) have been correlated with the regulation of tumor progression, cellular growth and differentiation in several malignant tumors. The objectives of this study were to clarify the role of IL-11 and IL-11Rα in human gastric carcinoma. IL-11 and IL-11Rα were studied in 73 cases of surgically resected human gastric adenocarcinomas by immunohistochemistry. The invasive activity and cell signaling pathway of gastric carcinoma cell lines were also examined. Among the 73 cases of adenocarcinoma, 53 (72.6%) and 47 cases (64.4%) showed positive staining in carcinoma cells for the IL-11 and IL-11Rα proteins, respectively. Histologically, IL-11 expression correlated only with Lauren's classification (p< 0.05). The expression of IL-11Rα correlated with the grade of tumor invasion (p< 0.05) and vessel infiltration (p< 0.01). All of the four gastric carcinoma cell lines expressed both IL-11 and IL-11Rα proteins in western blot analysis. Recombinant human IL-11 (rhIL-11) promoted the migration of SCH cells by the activation of the phosphatidylinositol-3 kinase pathway. Wortmannin diminished the promotion of chemotactic motility and invasive activity by rhIL-11. These findings suggest that the IL-11/IL-11R pathway plays an important role in the progression and the differentiation of human gastric carcinomas.