The quantitative analysis of lung collagen, the major extracellular matrix protein in lung fibrosis [1], with assays for Sirius red collagen-binding, hydroxyproline and collagen type 1 demonstrated that C/EBPβ-Ala217 mice were refractory to the development of lung fibrosis after exposure to the lung toxin (Figure 1C, 1D and 1E). This evidence concerns the gene CEBPB and pulmonary fibrosis.