OBJECTIVE: Hyaluronic acid is a naturally occurring glycosaminoglycan which, by virtue of its viscosity, elasticity and other theological properties, acts as lubrication and shock absorbing fluid in joints. In addition to its lubrication and cushioning properties, hyaluronic acid has been associated with in vitro anti-inflammatory activity and possible disease-modifying effect in animals. The purpose of this study was to evaluate the effect of intraarticular injection of hyaluronic acid or steroid on the healing of the experimental degenerative osteoarthritis and the therapeutic synergism between the hyaluronic acid and steroid. METHOD: 48 rabbits with experimental osteoarthritis produced by extension immobilization of knees were treated with hyaluronic acid and/or steroid and then assessed clinically, radiologically, scintigraphically and histopathologically at pre and post treatment. RESULTS: The hyaluronic acid treated group had more favorable results than other groups but the results were not statistically significant. The steroid treated group did not have significant change in comparison to the control group. Therapeutic synergism between hyaluronic acid and steroid was not found. CONCLUSIONS: The results of this study indicate that the intraarticular injection of hyaluronic acid may be effective for the treatment of patients with osteoarthritis.