Apoptosis of alveolar epithelial cells (AECs) is believed to be critical for the development of bleomycin (BLEO)-induced pulmonary fibrosis. Previous studies showed that apoptosis of alveolar epithelial cells in response to BLEO could be abrogated by antisense oligonucleotides against angiotensinogen (AGT) mRNA and requires angiotensin II (ANG II) synthesis de novo . In this study we hypothesized that blockade of local pulmonary ANG II synthesis by intratracheal (I.T.) administration of antisense oligonucleotides against AGT mRNA might attenuate BLEO-induced apoptosis of AECs and prevent pulmonary fibrosis. In a BLEO-induced rat model of lung fibrosis, endogenous lung AGT was upregulated in vivo as early as 3 hours after BLEO instillation, as detected by RT-PCR, in situ hybridization and immunohistochemistry. AGT mRNA and angiotensin peptides were localized in type II alveolar epithelial cells and also colocalized with alpha-smooth muscle actin (β-SMA), a marker of myofibroblasts. Tagged antisense administered I.T. was specifically accumulated by the lung relative to liver and kidney, and localized primarily in the epithelium of airways and cells within alveolar walls. The intratracheal AGT antisense reduced BLEO-induced pulmonary fibrosis measured by lung hydroxyproline assay, decreased lung AGT and active caspase-3 proteins, and reduced the number of apoptotic epithelial cells but had no effect on the serum ANG II concentration. These data are consistent with the hypothesis that lung-derived AGT and local pulmonary ANG II are required for BLEO-induced pulmonary fibrosis, and suggest the possibility of antisense-based manipulation of the local angiotensin system as a potential treatment of fibrotic lung diseases.