A characteristic feature of fibroblasts cultured from affected skin areas of patients with systemic sclerosis (SSc) and localized scleroderma (morphea) is excessive activation of collagen biosynthesis. To elucidate the nature of fibroblast activation in scleroderma we have studied the expression of 3 noncollagenous connective tissue components, osteonectin, small dermatan sulfate proteoglycan (proteoglycan II, decorin), and transforming growth factor-beta 1 (TGF-beta 1), by measuring their mRNA levels in fibroblast cultures from 6 patients with SSc and 3 with morphea. A clear correlation was observed between the increase in type I collagen and osteonectin mRNA in these cell lines. The apparent overproduction of osteonectin by scleroderma fibroblasts is in accordance with the suggested activation of osteonectin expression during tissue remodeling. The levels of decorin mRNA showed marked variation in the cell lines, but were in no correlation with collagen or osteonectin mRNA. The levels of TGF-beta 1 mRNA were found to be slightly elevated in fibroblasts grown from affected scleroderma skin. This may suggest that this potent activator of collagen production has a role during the initial activation of dermal fibroblasts both in SSc and morphea.