We examined c-sis, c-myc, and c-mybproto-oncogene expression in fibroblasts cultured from affected and unaffected skin of patients with systemic sclerosis (SSc), and from healthy donor skin. Total cellular RNA from cultured dermal fibroblasts was used in slot blot analysis and scanning densitometry or phosphorimaging to quantify steady-state levels of proto-oncogene mRNAs. PDGF B-chain levels in culture supematants of fibroblasts were determined by ELISA. Our results demonstrate that steady-state levels of c-mycand c-mybmRNA were elevated 1.5-to 5.6-fold in intralesional fibroblasts from SSc patients as compared to other cells examined. Levels of c-sismRNA and PDGF-B protein were comparable regardless of source. Elevated c-mycand c-mybexpression may be indicative of, and may contribute to, fibroblast activation in SSc.