Cardiopulmonary bypass (CPB) has been known to induce an inflammatory response that is influenced by various factors. Hypothermia is supposed to reduce inflammation after CPB. We developed an in vitro coculture model for CPB and compared the effects of hypothermia on the inflammatory response in the coculture model with results from a clinical prospective randomized trial. The coculture model consisted of endothelial cells and monocytes. Cells were stimulated with tumor necrosis factor (TNF)-α and exposed to deep hypothermia (20°C) or normothermia (37°C). In the clinical trial, 20 patients undergoing CPB for ventricular septum defect receive either normothermic (37°C) or mild hypothermic (32°C) CPB. We observed a significant interleukin (IL)-6 and IL-8 release in the coculture model 2 and 24 h after the experimental start. In the clinical trial, cytokines were significantly increased directly after weaning from CPB and remained elevated until 24 h. IL-8 and IL-6 secretions were similar in the hypothermic and normothermic group of the coculture model and the patients after 24 h. These results demonstrate that the inflammatory reaction observed in our coculture model is comparable with the cytokine increase in the blood of children undergoing CPB. Our coculture model could be useful for studies on the mechanisms of CPB-induced inflammation.