Objective: Several factors modulate fibroblast proliferation and collagen deposition in pulmonary fibrosis diseases, including cyclooxygenase (COX). The main of this study was observed the relationship between COX1 and COX2 in surgical lung biopsies from patients with idiopathic pulmonary fibrosis (IPF). Method: Twenty four patients (64±8.9 year) were characterized with IPF. Immunohistochemistry and histomorphometry were used to evaluate the amount of COX1 and COX2 expression in lung specimens. The expression of these markers was tested with their pulmonary function tests. Results: Significantly a higher amount of COX-2 was observed in IPF patients principally in normal and vascular areas (p=0.05) when compared with control group (Figure) , contrasting with similar amounts of COX-1 in both groups. An important negative correlation was observed between total lung COX-2 expression and DCO/VA (r=0.694, p=0.01) in IPF patients. Conclusion: Higher vascular expressions of COX2 probably mediated the inflammatory reaction in patients with IPF and have an important impact with pulmonary function tests, suggesting that a participation in the pathway of IPF. Financial Support: FAPESP.