Osteoarthritis is a joint disease that affects mainly articular cartilage, caused by wearing of the major components of its extracellular matrix: collagen and proteoglycans. To date, treatment of osteoarthritis has been mainly focused on alleviating the pain, without repairing the damage in the cartilage. However, since 1990 there is a growing interest in the so-called nutraceutic agents or nutrition supplements. In recent years, various substances have been identified to influence articular chondrocyte metabolism and thus alter matrix turnover. The aim of the present study was to investigate the effect of several amino acids on collagen biosynthesis by bovine articular chondrocytes and mice fibroblasts cultured in vitro. For this purpose, we have first examined the effect of basal culture media and of amino acid-enriched media on the synthesis and collagen secretion of collagen-producing cells. The results obtained show that addition of glycine, proline or lysine to the culture media enhances the biosynthesis and secretion of collagen in these cells. Since development of osteoarthritis seems to be associated with a decrease in collagen metabolism, we have assessed the activation and regeneration of collagen in the articular cartilage of patients with osteoarthrosis for who diet has been supplemented with these amino acids. The results demonstrate a great decrease of the symptoms, and a clear improvement of the health state in all the cases.