In synovial fluid, hyaluronic acid (HA) is an essential component for the lubrication of joints, thus preventing friction. The relationship between HA and joint friction is not unambiguously established yet. In the present study, the effect of the application of HA on the frictional coefficient in the temporomandibular joint was evaluated. After measuring the frictional coefficient in intact porcine joints (n = 10), the subsequent effect of phosphate-buffered saline (PBS) washing and gauze scouring and the application of HA was examined. Compared with the intact joint, the frictional coefficient was significantly larger after PBS washing and gauze scouring. Subsequent application of HA resulted in a significant decrease (50-75%) of the frictional coefficient. However, it did not recover to the same value as in the intact joints. Observations by scanning electron microscopy showed that after PBS washing, the amorphous layer of the articular cartilage was still intact, whereas it was partially collapsed after gauze scouring. In conclusion, the addition of HA did reduce the coefficient of friction under the experimental conditions in this study; the relevance to the clinical condition and the duration of the treatment effect in vivo require further investigation. (C) 2004 Wiley Periodicals, Inc.