Smad3 gene methylation level was strongly correlated with Smad3 mRNA expression (correlation coefficient: -0.84), whereas the extent of pulmonary fibrosis was weakly correlated with the Smad3 gene methylation level and Smad3 mRNA expression (correlation coefficients: -0.18 and 0.21, respectively). This evidence concerns the gene SMAD3 and pulmonary fibrosis.