Background YKL-40 is a chitinase-like protein present in serum of healthy subjects and its levels are increased in several human inflammatory diseases. The aim of this study was to evaluate the levels of both serum and sputum YKL-40 in cystic fibrosis (CF) patients. Methods Serum and sputum YKL-40 levels were measured in a cohort of twenty-eight patients with a diagnosis of CF and twenty healthy controls. Results Serum YKL-40 levels were significantly higher in CF patients (88.8±56.7 vs 18.6±2.9 ng/ml, P< 0.001), as well ...