Systemic sclerosis (SSc) is a fibroproliferative autoimmune disease characterized by the excessive production and deposition of collagen in skin and internal organs. Acting through specific transmembrane receptors, transforming growth factor-? (TGF-?) is known to play a crucial role in the development of tissue fibrosis. The authors had previously identified several signaling molecules other than Smad proteins including protein kinase C-d (PKC-d) as candidates downstream of TGF-? receptors. The aim of the present study was to examine the possible role of PKC-d in the upregulation collagen gene expression in SSc dermal fibroblasts.