41 patients were randomized to three weekly injections of either hyaluronic acid (Orthovisc) or placebo (0.9% NaCl). The purpose of this study was the evaluate and compare cytokine levels - interleukin-6, interleukin-8, and tumour necrosis factor-alpha - in the synovial fluid between groups at one week after the completion of treatment. Additionally, the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC), knee effusion, knee swelling, and knee range of motion were assessed. The results indicated that IL-6 levels decreased to a significantly greater degree in the HA group compared to control group though no significant within-group changes were detected for IL-8 and TNF-a levels.