Caffeine (1,3,7-trimethylxanthine), the active principle alkaloid of coffee (Coffea arabica) and tea (Camellia sinensis) possesses a restraining effect on tumor-induced suppression of the specific immune response in adult mice. The present study deals with the effect of long-term consumption of caffeine in the development of Ehrlich ascites carcinoma (EAC) cells in adult Swiss female mice, in relation to the innate immune response and tumor growth. Although the consumption of caffeine alone for more than 12 consecutive days did not affect the innate immune response parameters, continuation of its treatment following intraperitoneal EAC cell inoculation not only reduced the in vivo tumor growth but also reduced/restored the EAC cell-induced suppression of the innate immune response. These results suggest that caffeine may inhibit in vivo tumor growth through reduction of the cancer cell-induced suppression of the innate immune response. Georg Thieme Verlag KG Stuttgart.