Transforming growth factor-β1 (TGF-β1) is a multifunctional cytokine that induces mesenchymal cell proliferation in vivo while inhibiting growth of most cells directly via serine-threonine receptor(s) binding/activation in vitro. In this study, the ability of TGF-β1 to regulate the receptor expression of classical mitogenic growth factors that bind receptor tyrosine kinases was examined. TGF-β1 markedly increased the protein expression of the fibroblast growth factor (FGF) receptors FGFR-1 (Flg) and FGFR-2 (Bek) in a time- and dose-dependent manner in human lung fibroblasts. This resulted in a potentiation of the mitogenic response of multiple FGF ligands that bind to these receptors. TGF-β1 had no effect on epidermal growth factor (EGF) or platelet-derived growth factor (PDGF)-β receptor expression and the mitogenic responses mediated by specific ligands for these receptors were not increased. These results demonstrate a novel action of TGF-β1 to selectively upregulate the expression of FGF receptor family members leading to enhanced mitogenesis by FGFs.