Hyaluronic acid (HA), also known as hyaluronan or hyaluronate is synthesized by fibroblasts and other specialized connective tissue cells and is a major component of connective tissues and thus distributed ubiquitously in the organism. HA can act as a biomarker for joint diseases and correlates in RA and OA patients with the degree of joint inflammation, synovial proliferation and the degree of joint space narrowing. Due to the decreased capacity for hyaluronan clearance, HA is an important biomarker for most chronic liver diseases which are characterised by fibrosis and cirrhosis. Our Hyaluronic Acid PLUS ELISA is suited for the determination of hyaluronic acid in plasma, serum and other biological fluids.