BACKGROUND: It is well known that various cytokines and growth factors secreted mainly from alveolar macrophages do the key role in the pathogenesis of IPF. But recently it has been known that structural cells like fibroblast can also release cytokines. So the phenotypic changes in fibroblasts of IPF may do a role in continuous progression of fibrosis. The aim of this study is to find out whether there is a change in the biologic properties of the lung fibroblasts of IPF. SUBJECTS AND METHOD: The study was done on 13 patients with IPF diagnosed by open or thoracoscopic lung biopsy and 7 control patients who underwent resectional surgery for lung cancer. Lung fibroblast cell lines (FB) were established by explant culture technique from the biopsy or resected specimen RESULT: Basal proliferation of the fibroblast of IPF(IFB) measured by BrdU uptake tended to be highter than control fibroblast(NFB) (0.212+/- 0.107 vs 0.319+/-0.143, p= 0.0922), also there was no signifrcant difference in proliferation after the stimulation with PDGF or 10% serum. On the contrary, the degree of inhibition in proliferation by PGE2 was significantly lower(33.0+/-13.1%) in IFB than control(46.7+/-10.0%, p= 0.0429). The IFB secreted significantly higher amount of MCP-1(1574+/-1283 pg/ml) spontaneously than NFB(243+/-100 pg/ml) and also after the stimulation with TGF-beta (3.23+/-1.31 ng/ml vs 0.552+/-0.236 ng/ml, p= 0.0012). Similarly IL-8 and IL-6 seretion of IFB was significantly higher than NFB at basal state and with TGF-beta stimulation. But after the maximal stimulation with IL-1beta, no significant difference in cytokine secretion was found between IFB and NFB. CONCLUSION: Above data suggest that the fibroblasts of IPF were phenotypically changed and these change may do a role in the pathogenesis of IPF.