Background: How elevated temperature is generated during airway infections represents a hitherto unresolved physiological question. We hypothesized that innate immune defence mechanisms would increase luminal airway temperature during pulmonary infection. Methods: We determined the temperature in the exhaled air of cystic fibrosis (CF) patients. To further test our hypothesis, a pouch inflammatory model using neutrophil elastase-deficient mice was employed. Next, the impact of temperature changes on the dominant CF pathogen Pseudomonas aeruginosa growth was tested by plating method and RNAseq. Results: Here we show a temperature of ~38°C in neutrophil-dominated mucus plugs of chronically infected CF patients and implicate neutrophil elastase:α₁-proteinase inhibitor complex formation as a relevant mechanism for the local temperature rise. Gene expression of the main pathogen in CF, P. aeruginosa, under anaerobic conditions at 38°C vs 30°C revealed increased virulence traits and characteristic cell wall changes. Conclusion: Neutrophil elastase mediates increase in airway temperature, which may contribute to P. aeruginosa selection during the course of chronic infection in CF.