Immunohistochemical analysis using 24 different monoclonal and polyclonal antibodies was applied to lung biopsy and autopsy material from 9 patients with idiopathic pulmonary fibrosis (IPF) and 6 patients without lung disorders as control. Lymphoid, non-lymphoid cells and their subsets as well as extracellular matrix (fibronectin, laminin and collagens type I, III and IV) were observed in lung interstitium. Our results suggest that local B and T lymphoid immune responses are occurring in IPF. Extracellular matrix alterations are closely linked with the local immune responses.