Technical Abstract: A variety of fruits have traditionally been used in Asian cultures to enhance innate immunity and treat cancers. However, limited information exists on the underlying mechanisms responsible for these immune enhancing properties. The present investigation was conducted to examine the effects of methanol extracts of three Korean indigenous fruits (the persimmon, the raspberry, and the tomato) on various in vitro parameters of immune activation (lymphocyte proliferation, nitric oxide production by macrophages) and tumor cells. The chicken model was used in this study since its innate immune system has been well characterized. Co-culture of persimmon (Diospyros kaki) as well as tomato (Lycopersicon esculentum) extracts with chicken spleen lymphocytes in vitro induced a significant proliferation of lymphocytes. Stimulation of chicken macrophages with extracts of raspberries (Rubus crataegifolius), but not persimmons and tomatoes, resulted in significantly high nitric oxide production at a level similar to that induced by interferon '. More importantly, all fruit extracts tested in this study significantly inhibited chicken tumor cell growth, which was compared with vehicle control (p < 0.05). These results, for the first time, showed clear evidence that traditional Korean medicinal fruits such as persimmons, raspberries, and tomatoes possess immunostimulating components which not only stimulate innate immunity, but also inhibit tumor cell growth in chickens. This finding provides a rationale for further studies on these fruits in both human and other animal models.