PTX3 plasma levels were analysed in P. Aeruginosa infected CF patients at admission to the hospital for revaluation and antibiotic treatment, and end of hospitalization. Results obtained indicate that PTX3 levels were increased in all patients, in comparison to the value considered normal in healthy donors, however, the analysis did not reveal statistical significant associations between PTX3 levels and clinical parameters. In only one patient PTX3 levels were below the normal value (2 ng/ml) both at admission and discharge, suggesting defective PTX3 production. PTX3 levels were not detectable in breath samples. The analysis of the production of PTX3 and IL-8 by monocytes collected from CF patients showed that most patients (7/9) poorly responded to bacteria stimulation and did not produce increased levels of PTX3 upon stimulation. These results are in agreement with previous studies suggesting a state of tolerance to LPS of CF monocytes. The analysis of PTX3 plasma levels is potentially useful in identifying defective production of PTX3 in CF patients and improving the transfer to the clinic of PTX3 as therapeutic molecule.