In all three investigated groups, a strong significant correlation was found for sputum periostin concentration at protein and mRNA expression levels: r = 0.98, p < 0.001 for asthma; r = 0.91, p < 0.001 for COPD; and r = 0.79, p < 0.001 for controls. This evidence concerns the gene POSTN and chronic obstructive pulmonary disease.