It is known that thymidine phosphorylase (dThdPase) is increased in various types of malignant tumors and is induced by cytokines. In this study, we have investigated the effects of OK-432, which induces multiple cytokines, on dTHdPase expression and angiogenesis in human gastric carcinomas. We examined 25 patients who underwent gastrectomy for gastric carcinoma. OK-432 was directly injected in tumors in 16 (OK group) of 25 patients via endoscopy before operation and the other 9 patients were not treated (control group). The dThdPase activity in carcinoma tissues of the OK group was significantly higher than that of the control group (P < 0.05). The amounts of IL-1 alpha, IFN-alpha, and IFN-gamma in carcinomas in the OK group were significantly higher than in the controls (P < 0.05), and these were significantly correlated with the dThdPase activity. Intratumoral OK-432 administration enhances the expression of dThdPase in gastric carcinoma cells by inducing various cytokines.