We examined the interaction between scirrhous gastric cancer cells and organ-specific fibroblasts in vivo and in vitro. Co-inoculation of scirrhous gastric cancer cells with gastric fibroblasts into nude mice specifically increased tumorigenicity, compared with that of gastric cancer cells alone. Furthermore, the histologic findings of the xenograft produced by co-inoculation with gastric fibroblasts was similar to that of human scirrhous gastric carcinoma. Conditioned medium from gastric fibroblasts significantly stimulated the growth of gastric cancer cells. These findings suggest that the growth of scirrhous gastric cancer cells was affected by orthotopic fibroblasts.