Hyaluronic acid is a natural component of cartilage and is considered not only as a lubricant in joints but also as playing a physiological role in the trophic status of cartilage. Hyalectin, a selected fraction of hyaluronic acid extracted from cocks' combs, has exhibited efficacy in animal models of osteoarthritis. To assess the efficacy and tolerability of intra-articular injections of hyalectin, we conducted a prospective, randomized, placebo-controlled trial of 1 years' duration in 110 patients with painful hydarthrodial osteoarthritis of the knee. At entry and once a week for 3 weeks, aspiration of the knee effusion and intra-articular injections of either hyalectin 20 mg (H) or its vehicle (C) were performed. The vehicle acted as the control treatment. Four weeks after the last injection, the improvement was greater in the H group compared with the C group (pain: -35.5 +/- 26.4 mm vs -25.8 +/- 21.4, P = 0.03, Lequesne's functional index: -3.8 +/- 4.3 vs -2.3 +/- 3.3, P = 0.03). During the 1 year follow-up, the need to perform supplementary local therapies (joint fluid aspiration because of painful hydarthrodial episodes and/or local corticosteroid injections) was more frequent in group C (44% vs 30%, P = 0.03). Moreover, at the final visit, the physician's overall assessment of efficacy was in favor of H (77% vs 54%, P = 0.01) and the improvement in the functional index was greater in group H (-4.4 +/- 5.1 vs -2.7 +/- 4.1, P = 0.05). This study suggests that intra-articular injections of hyalectin may (1) improve clinical condition and (2) have a long-term beneficial effect in patients with osteoarthritis of the knee.