Previous reports have shown that tumor necrosis factor alpha (TNF-alpha) controls the functions of fibroblasts cells, such as proliferation, cell migration and secretion of factors. The signaling for the biological effects of this and other cytokines is usually exerted through cell surface receptors. In this study, we demonstrated the presence of a surface and soluble TNF receptor in MRC5 fibroblasts. The presence of TNFRI and TNFRII mRNA was demonstrated by reverse-transcriptase-PCR (RT-PCR). Both surface TNFRI and TNFRII are expressed and the number of both membrane receptors is 9,251 sites per cell. Using TNF receptor specific antibodies and flow cytometry, we showed that MRC5 cells express mainly TNFRI.