The synthesis of collagen and its deposition into the extracellular matrix were studied in scleroderma and normal skin fibroblast cultures using immunocytochemistry, electron microscopy and electrophoretic analysis. Indirect immunofluorescence localized type I collagen to intracellular granules of normal skin fibroblasts but not to the extracellular matrix. A 48-h ascorbic acid-treatment of scleroderma and normal skin fibroblasts induced the appearance of fibrillar, collagen-containing deposits in the extracellular space as indicated by indirect immunofluorescence and electron microscopy. Interestingly, similar type I collagen-containing fibrils were observed in cultures of scleroderma skin fibroblasts even without preceding ascorbic acid treatment. Electrophoretic analysis revealed that ascorbic acid increases the conversion of procollagen to collagen to same extent both in scleroderma and control cell layers. The accumulation of collagen to the cell layer of scleroderma fibroblasts was increased when compared to normal skin fibroblasts; whereas the relative conversion of procollagen to collagen was identical in scleroderma and normal fibroblasts. The results show that the conversion of procollagen to collagen in the cell layers of both scleroderma and normal skin fibroblasts is dependent on ascorbic acid, due to improved secretion of procollagen molecules in the presence of ascorbic acid.