['Cardiac surgery with cardiopulmonary bypass (CPB) induces substantial release of IL-10, indicating increased Th2 cell response. Therefore, in this study, we wanted to verify if this response is due to CPB or surgical trauma, and to study its relation to postoperative effusions and edema (POEE) in children.', 'Th1/Th2 reaction was monitored in children undergoing cardiovascular surgery with (n = 75) and without CPB (n = 29).', 'Surgery with CPB compared to surgery without CPB induced a transient shift towards Th2. Elevated Th2 response was related to increased vascular permeability and POEE.'] Does transient Th1/Th2 disbalance indicate postoperative effusions and edema after cardiopulmonary bypass in children?