The nature of the participation of neutrophils in the post-cardiopulmonary bypass (CPB) inflammatory response is not very clear. The aim of our study was to investigate alterations in neutrophil phagocytic activity and adhesion molecule expression on these cells in children during and after CPB. Twenty-one children aged 6?33 months with congenital heart disease, scheduled for primary corrective surgery, were enrolled. The expressions of CD11b adhesion molecules and Fcg receptor on neutrophils and their phagocytic activity were evaluated. The studied markers were sequentially measured before, at the initiation of, and after CPB. During the course of the operation, CD11b molecule expression on neutrophils showed a slight elevation at the start of CPB (876.5104.8 mean fluorescence intensity, MFI, vs. 768.1178.2; p=0.0047), followed by a significant decrease to 689.01166.7 MFI after completion of the procedure. The expression of CD11b molecule on neutrophils measured at the end of CPB inversely correlated with the duration of CPB (r= ?0.68, p=0.00059). The expression of CD16 antigen dropped significantly at the start of CPB (1164.6307.3 MFI vs. 1327.4345.3 MFI; p=0.0007) and remained decreased until the end of CPB (814.0198.1 MFI). These findings suggest that the characteristics of the neutrophil response to cardiac surgery appear to depend on many factors. We demonstrated a link between the duration of CPB and adhesion molecule expression on neutrophils.