Standard methods of glycosaminoglycan separation were used to confirm the presence of hyaluronic acid in sheep and rabbit articular cartilage. During incubation of carilage in vitro in the presence of [1-14 C]acetate, cartilage cells synthesize this macromolecule and, under the conditions used, it appears to have a shorter turnover time than chondroitin suplhate in the same tissue. The possible functions of hyaluronic acid in cartilage are discussed.