Fibrotic ILDs, particularly IPF reporting the lowest concentrations of KL‐6 values in BAL and conversely the highest on serum, showed a substantially opposite pattern of KL‐6 expression: this is probably related to the architectural distortion of lung parenchyma due to fibrogenesis and to the augmented permeability of alveolar‐capillary membrane induced by inflammation, which led to an increased release of KL‐6 in the bloodstream. The gene discussed is MUC1; the disease is idiopathic interstitial pneumonia.