Scleroderma is a fibrotic disease occurring in a localized or systemic form. Disturbed regulation of connective tissue metabolism plays an important role in its pathogenesis. However, until now, most of the data available were obtained from studies of fibroblasts in culture and there is considerable doubt that fibroblasts in a monolayer reflect the in-vivo situation. Using in-situ hybridization with specific antisense RNAs on frozen sections of skin, cells were detected displaying enhanced messenger RNA levels for type I and type III collagen in patients with localized and systemic scleroderma. Activated fibroblastic cells were often located near blood vessels in the deep dermis of patients with early stages of the disease and were mostly surrounded by mononuclear cells. These findings are in agreement with the concept that the interaction of fibroblasts with 'immunocompetent cells' is crucial in the initial activation of connective tissue metabolism in fibrosis.