Decorin mRNA levels, the content of decorin and the synthesis of dermatan sulphate in skin fibroblasts from patients with systemic and localized scleroderma were investigated. Approximately a 2.2-fold increase in decorin mRNA levels, was found by Northern blot analysis in localized scleroderma, but no significant changes were found in systemic scleroderma. Decorin, as measured by an immunoblot assay, was increased 2.6-fold in fibroblast cultures from localized scleroderma but not in those from systemic scleroderma. In contrast, the synthesis of dermatan sulphate was similar in both conditions. These results indicate that altered decorin gene expression causes abnormal proteoglycan metabolism in localized scleroderma.