Fibroblast migration, proliferation, extracellular matrix protein synthesis and degradation,all of which play important roles in inflammation, are them selves induced by various growth factors and cytokines. Less is known about the interaction of these substances on lung fibroblast function in pulmonary fibrosis.The goal of this study was to investigate the effects of PDGF alone and in combination with IL–1β and TNF–α on the production of human lung fibroblast matrix metalloproteinases, proliferation, and the chemotactic response. The assay for MMPs activity against FITC labeled type I and IV collagen was based on the specificity of the enzyme cleavage of collagen. Caseinolytis and gelatinolytic activities of secreted proteinases were analyzed by zymography. Fibronectin in conditioned media was measured using human lung fibronectin enzyme immunoassay. Cell proliferation was measured by 3H-Thymidine incorporation assay. Cell culture supernatants were tested for PGE2 content by ELISA. Chemotactic activity was measured using the modified Boyden chamber.Matrix metalloproteinase assay indicated that IL–1β, TNF–α and PDGF induced intestitial collagenase (MMP-1) production. MMP assay also indicated that IL–1β and TNF–α had inhibitory effects on MMP-2,9(gelatinaseA,B) production. Casein zymography confirmed that IL–1β stimulated stromlysin (matrix metalloproteinase 3; MMP–3) and gelatin zymography demonstrated that TNF–α induced MMP–9 production in human lung fibroblast, whereas PDGF alone did not. PDGF in combination with IL–1β and TNF–α induced MMP–3 and MMP–9 activity, as demonstrated by zymography. PDGF stimulated lung fibroblast proliferation in a concentration-dependent manner, whereas IL–1β and TNF–α alone had no effect. In contrast, the proliferation of human lung fibroblasts by PDGF was inhibited in the presence of IL–1β and TNF–α, and this inhibition was not a consequence of any elevation of PGE2. PDGF stimulated fibroblast chemotaxis in a concentrationdependent manner, and this stimulation was augmented by combining PDGF with IL–1β and TNF–α.These findings suggested that PDGF differentially regulated MMPs production in combination with cytokines, and further that MMP assay and zymography had differential sensitivity for detecting MMPs. The presence of cytokines with PDGF appears to modulate the proliferation and chemotaxis of human lung fibroblasts.