Background: Our main objective was to evaluate the ability of cranberry phytochemicals to modify immunity, specifically gamma delta -T cell proliferation, after daily consumption of a cranberry beverage, and its effect on health outcomes related to cold and influenza symptoms. Methods: The study was a randomized, double-blind, placebo-controlled, parallel intervention. Subjects drank a low calorie cranberry beverage (450 ml) made with a juice-derived, powdered cranberry fraction (n=22) or a placebo beverage (n=23), daily, for 10 wk. PBMC were cultured for six days with autologous serum and PHA-L stimulation. Cold and influenza symptoms were self-reported. Results: The proliferation index of gamma delta -T cells in culture was almost five times higher after 10 wk of cranberry beverage consumption (p0.001). In the cranberry beverage group, the incidence of illness was not reduced, however significantly fewer symptoms of illness were reported (p=0.031). Conclusions: Consumption of the cranberry beverage modified the ex vivo proliferation of gamma delta -T cells. As these cells are located in the epithelium and serve as a first line of defense, improving their function may be related to reducing the number of symptoms associated with a cold and flu.