BACKGROUNDS: The injury of a tissue results in the infalmmation, and the imflammed tissue is replaced by the normal parenchymal cells during the process of repair. But, constitutional or repetitive damage of a tissue causes the deposition of collagen resulting in the loss of its function These lesions are found in the lung of patients with idiopathic pulmonary fibrosis, complicated fibrosis after diffuse alveolar damage (DAD) and inorganic dust-induced lung fibrosis. The tissue from lungs of patients undergoing episodes of active and/or end-stage pulmonary fibrosis shows the accumulation of inflammatory cells, such as mononuclear cells, neutrophils, mast cells and eosinophils, and fibroblast hyperplasia. In this regard, it appears that the inflammation triggers fibroblast activation and proliferation with enhanced matrix synthesis, stimulated by inflammatory mediators such as interleukin-1 (lL-1) and/or tumor necrosis factor (TNF). It has ken well known that TGF-beta enhance the proliferation of fibroblasts and the production of collagen and fibronectin, and inhibit the degradation of collgen. In this regard, It is likely that TGF-beta undergoes important roles in the pathogenesis of pulmonary fibrosis. Nevertheless, this single cytokine is not the sole regulator of the pulmonary fibrotic response. It is likely that the balance of many cytokines including TGF-beta, IL-1, IL-6 and TNF-alpha regulates the pathogenesis of pulmonary fibrosis. In this study, we investigate the interaction of 'PGF-beta, IL-1beta, IL-6 and TNF-alpha and their effect on the proliferation of fibroblasts. METHODS: We used a human fibroblast cell line, MRC-5 (ATCC). The culture of MRC-5 was confirmed by immunofluorecent staining. First we determined the concentration of serum in cuture medium, in which the proliferation of MRC-5 is supressed but the survival of MRC-5 is retained. Second, we measured optical density after staining the cytokine-stimulated cells with 0.5% naphthol blue black in order to detect the effect of cytokines on the proliferation of MRC-5. RESULT: In the medium containg 0.5% fetal calf serum, the proliferation of MRC-5 increased by 50%, and it was maintained for 6 days. IL-1beta, TNF-alpha and IL-6 induced the proliferation of MRC-5 by 45%, 160% and 120%, respectively. IL-1beta and TNF-a enhanced TGF-beta-induced proliferation of MRC-5 by 64% and 159%, but IL-6 did not affect the TGF-beta-induced proliferation. And TNF-alpha-induced proliferation of MRC-5 was reduced by IL-1beta in 50%. TGF-beta, TNF-alpha and both induced the proliferation of MRC-5 to 89%, 135% and 222 %, respectively. CONCLUSIONS: TNF-alpha TGF-beta and lL-1beta, in the order of the effectiveness, showed the induction of MRC-5 proliferation of MRC-5. TNF-alpha and IL-1beta enhance the TGF-beta-induced proliferation of MRC-5, but IL-6 did not have any effect. TNF-alpha-induced proliferation of MRC-5 is diminished by IL-i, and TNF-alpha and TGF-beta showed a additive effect.