We investigated the responses of normal and scleroderma fibroblasts to various growth Factors, especially transforming growth factor-β1 (TGF-β1). The effects of various growth Factors on [³H]thymidine incorporation in normal and scleroderma fibroblasts were examined. [^125KI]-labeled platelet-derived growth factor (PDGF)-BB binding in scleroderma and normal fibroblasts was examined both in the presence and absence of TGF-β1 (1 ng/ml). Cytoplasmic protein was isolated and analyzed by Western blotting. Total RNA from fibroblasts was also isolated and analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) using specific primer sets. Mitogenic responses to TGF-β1 (0.33-1 ng/ml) in seven scleroderma fibroblast strains were significantly greater than those in normal controls. [^125KI]-PDGFBB binding to scleroderma fibroblasts was increased after TGF-β1 stimulation. The increased response to TGF-β1 was shown to be mediated through PDGFlike protein induction; TGF-βl-treated scleroderma fibroblasts produced greater amounts of 36-kD PDGF-like protein, which was reported previously as connective tissue growth Factor (CTGF), than did TGF-β1-treated normal fibroblasts. TGF-β1 treatment also upregulated PDGF-α receptor expression in scleroderma fibroblasts but not in normal dermal fibroblasts, mRNA expression of CTGF and PDGF-α receptor was correlated with the above protein expression. These observations suggest that the increased growth response to TGF-β1 in scleroderma fibroblasts is mediated through the induction of CTGF and PDGF-α receptor.