OBJECTIVES: The primary aim of this prospective study was to perform a comprehensive serial characterisation of monocyte and neutrophil function, circulating monocyte subsets, and bronchoalveolar lavage (BAL) fluid after lung resection. A secondary aim was to perform a pilot, hypothesis-generating evaluation of whether innate immune parameters were associated with postoperative pneumonia. METHODS: Forty patients undergoing lung resection were studied in detail. Blood monocytes and neutrophils were isolated preoperatively and at 6, 24 and 48 h postoperatively. BAL was performed preoperatively and immediately postoperatively. Monocyte subsets, monocyte responsiveness to lipopolysaccharide (LPS) and neutrophil phagocytic capacity were quantified at all time points. Differential cell count, protein and cytokine concentrations were measured in BAL. Pneumonia evaluation at 72 h was assessed using predefined criteria. RESULTS: After surgery, circulating subsets of classical and intermediate monocytes increased significantly. LPS-induced release of proinflammatory cytokines from monocytes increased significantly and by 48 h a more proinflammatory profile was found. Neutrophil phagocytosis demonstrated a small but significant fall. Factors associated with postoperative pneumonia were: increased release of specific proinflammatory and anti-inflammatory cytokines from monocytes; preoperative neutrophilia; and preoperative BAL cell count. CONCLUSIONS: We conclude that postoperative lung inflammation is associated with specific changes in the cellular innate immune response, a better understanding of which may improve patient selection and prediction of complications in the future.