Growth kinetics and collagen production were determined in smooth muscle cells isolated from human jejunum and maintained in cell culture. Collagen synthesis increased during the first 15 days in culture at a time when the rate of cell proliferation was maximal. When confluent, these cells produced significantly more collagen than human dermal fibroblasts cultured under identical conditions. The smooth muscle cells required daily replenishment of ascorbate for maximal collagen synthesis. The types of collagen produced by human intestinal smooth muscle cells in culture were the same as those collagens extracted from strictured human bowel (types I, III, and V). These findings suggest that collagen production by human intestinal smooth muscle cells has a role in the repair as well as the fibrosis of the gastrointestinal tract. © 1987.