We hypothesized that formation of pulmonary emphysema could be diminished after previous activation of stem cells. Animals received either a daily dose of the hematopoietic growth factors (GF; recombinant rat stem cell factor plus recombinant granulocyte colony stimulating factor; n=6, Elastase/GF group) or vehicle (n=9, Elastase/Sham group) starting 3 days before intratracheal instillation of elastase or vehicle and continued for another 25 days. Control animals were treated with NaCl (n=9, Sham/Sham group). On day 25, in all animals, a 2-mL pump was implanted subcutaneously that delivered 200 microg/h 5-bromo-2-desoxyuridine (BrdU) until study termination. Compared to controls, the Elastase/Sham group exhibited elevated total lung capacity (TLC) and functional residual capacity (FRC), significantly increased mean free alveolar pathway, alveolar volume, and decreased septal density. The Elastase/GF group showed (1) a significant increase of TLC and FRC, (2) a significant increase in alveolar size and volume, (3) a significant reduction of septal density, volume, and thickness. Proliferation in lung parenchyma and in terminal bronchioles remained significantly decreased in the Elastase/Sham group and the Elastase/GF group. Blood cell number has significantly increased in the Elastase/GF group. The application of GF-enhanced pulmonary emphysema, presumable because of increased inflammatory activity, was a result of a preventive treatment.