Systemic sclerosis is an autoimmune disease characterized by accumulation of connective tissue components, particularly type I collagen, in the skin and internal organs. Turnover of the collagenous extracellular matrix (ECM) is dependent on the balance between collagenases and their specific tissue inhibitors (TIMPs). To elucidate the role of TIMPs, especially the new ECM bound TIMP-3 and also soluble TIMP-1 and -2 in the pathogenesis of dermal fibrosis, we have studied their expression in nonaffected and scleroderma skin fibroblasts from 7 patients with systemic sclerosis. In 5 of 7 scleroderma fibroblasts lines TIMP-3 mRNA expression was elevated simultaneously with type I collagen mRNA levels, as compared to nonaffected fibroblasts. TIMP-1 expression was elevated in 3 of these 5 scleroderma cell lines but no specific changes in TIMP-2 expression was noticed. We also examined TIMP-3 and -1 expression in fibrotic lesions from patients with scleroderma using in situ hybridizations. Expression of TIMP-3 mRNA was detected in 7 of 12 scleroderma skin samples in dermal fibroblasts surrounded by abnormally thickened collagen fibers and inflammatory cells. No expression of TIMP-3 was detected in dermal layer of normal skin. TIMP-1 mRNA was expressed in 3 of 8 scleroderma skin samples both in fibroblasts and in endothelial cells. No collagenase-1 (MMP-1) mRNA was detected in any of these samples. This study shows increased expression of TIMP-3 mRNA in activated scleroderma fibroblasts in culture and in vivo suggesting that TIMP-3 may participate in development of dermal fibrosis via inhibition of turnover of fibrotic ECM.