Background: Hypersensitivity pneumonitis ( HP) is an interstitial lung disease caused by repeated inhalations of finely dispersed organic particles or low molecular weight chemicals. The disease is characterized by an alveolitis sustained by CD8(+) cytotoxic T lymphocytes, granuloma formation, and, whenever antigenic exposition continues, fibrosis. Although it is known that T-cell migration into the lungs is crucial in HP reaction, mechanisms implicated in this process remain undefined. Methods: Using flow cytometry, immunohistochemistry, confocal microscopy analysis and chemotaxis assays we evaluated whether CXCL10 and its receptor CXCR3 regulate the trafficking of CD8(+) T cells in HP lung. Results: Our data demonstrated that lymphocytes infiltrating lung biopsies are CD8 T cells which strongly stain for CXCR3. However, T cells accumulating in the BAL of HP were CXCR3(+)/ IFN gamma(+) Tc1 cells exhibiting a strong in vitro migratory capability in response to CXCL10. Alveolar macrophages expressed and secreted, in response to IFN-gamma, definite levels of CXCL10 capable of inducing chemotaxis of the CXCR3(+) T-cell line. Interestingly, striking levels of CXCR3 ligands could be demonstrated in the fluid component of the BAL in individuals with HP. Conclusion: These data indicate that IFN-gamma mediates the recruitment of lymphocytes into the lung via production of the chemokine CXCL10, resulting in Tc1-cell alveolitis and granuloma formation.