['Gaining asthma control is still a challenge in a large number of patients. It could be facilitated by using biomarkers indicating the grade of inflammation and correlating with clinical picture. Chitinases and chitinase-like proteins play a role in Th2-type inflammation. Thus, they may be useful in diagnosing and monitoring of asthma.', 'The aim of the study was to investigate the relevance of YKL-40 as a good biomarker of asthma, its control, and severity.', "Level of YKL-40 was determined by means of immunoassay in sera of 59 asthmatics (39 women, 20 men, aged 23-76 years) and 29 healthy controls (18 women, 11 men, aged 20-80 years). Asthma severity and control were assessed according to GINA guidelines. Differences between groups were compared with the use of Mann-Whitney's U-test. Correlations between variables were assessed with Pearson's test.", 'Symptoms of asthma were found to be controlled in 12 (20%), partly controlled in 17 (29%), and uncontrolled in 30 (51%) patients. YKL-40 levels were significantly higher, on average, in asthmatics compared to control group (median levels: 125.3 U and 84.1 U, respectively, p < .001). YKL-40 correlated with the number of blood eosinophils (r = 0.376, p = 0.05). However, no relations have been found between YKL-40 level and asthma severity, control, or total serum IgE (r = -0.05, p = .05).'] Is yKL-40 protein a marker of asthma?