Morphometric analysis using a digital image analyzer system clearly revealed the decrease of immunoreactivity for thrombomodulin compared to CD34 in the autopsied lung tissues of IPF patients died after acute exacerbation (26.1 ± 7.2%, n = 8) in comparison with controls (89.7 ± 13.8%, n = 3) and even with the biopsied lung tissues from stable IPF patients (66.5 ± 9.0%, n = 10). This evidence concerns the gene CD34 and idiopathic pulmonary fibrosis.