Using an agarose gel culture system, the response of adult human chondrocytes to prolonged exposure of ascorbic acid was evaluated using histochemical, immunocytochemical and morphological techniques. The response of these cells to ascorbic acid was different from those previously reported in the literature. Many chondrocytes branched within the agarose gel with continued exposure to ascorbic acid while other chondrocytes maintained a round configuration typical of chondrocytes in vivo. Fibronectin and type I collagen were closely associated with the cell processes of the branching cells. Type II collagen and an alcian blue-staining matrix were associated with the rounded cells but not with the branched cells. These data suggest that the chondrocytes are able to express both dedifferentiated and redifferentiated phenotypes with ascorbic acid under these culture conditions. In addition, human chondrocytes were cultured in a collagen gel and began branching within 1 hour of culture. It is possible that an accumulation of type I collagen in the pericellular matrix of ascorbic acid treated cultures may enhance and explain the branching seen in these cultures. Studies by others have indicated that ascorbic acid may enhance, reduce, and/or modify the cartilage matrices produced by chondrocytes. These controversial reports in the literature are presumably due to variations between species and the culture methods employed.