An enzyme immunoassay for the quantitative determination of beta-2 microglobulin (B2MG) concentration in serum. Beta-2-microglobulin (Beta2-MG) is expressed by the nucleated cells of the body and on many tumor lines. Human Beta2-MG is a low molecular weight protein (MW 11600) consisting of a single polypeptide chain of 99 amino acids. It is identical to the small chain of the HLA-A, -B, and -C major histocompatibility complex antigens. In structure and amino acid sequence, it resembles the CH3 region of IgG, though it is antigenically distinct. Beta2-MG is eliminated via the kidneys. After filtration through the glomeruli, it is reabsorbed and catabolized by the proximal tubular cells through endocytosis. It is found at low levels in the serum and urine of normal individuals. Typically only trace amounts of Beta2-MG are excreted in the urine and higher rates are interpreted as evidence of tubular dysfunction. Urinary excretion is markedly increased in tubulointerstitial disorders, and where aminoglycosides and anti-inflammatory compounds are present. Beta2-MG is also excreted in increased amounts in the urine of patients with upper urinary tract infections and connective-tissue diseases such as rheumatoid arthritis and Sjogren’s syndrome. Elevated serum concentrations in the presence of normal glomerular filtration rate suggest increased Beta2-MG production or release. In patients with rheumatoid arthritis, systemic lupus erythematosus, sarcoidosis and some viral diseases including cytomegalovirus, non-A and non-B hepatitis and infectious mononucleosis, the Beta2-MG serum level changes in relation to disease activity. The Beta2-MG ELISA provides a sensitive and reliable assay for the measurement of Beta2-microglobulin in human serum. The kit features a standard range of 0.625 to 10 µg/mL and will determine a minimum detectable concentration of 0.1 µg/mL. The assay provides results in less than 2 hours in a microtiter plate format. The Beta2-MG ELISA test is based on the principle of a solid phase enzyme-linked immunosorbent assay (ELISA). The assay system utilizes a monoclonal anti-Beta2-MG antibody for solid phase immobilization (on the microtiter wells). A sheep anti-Beta2-MG antibody is in the antibody-enzyme (horseradish peroxidase) conjugate solution. The diluted test sample is allowed to react first with the immobilized antibody for 30 minutes at 37 °C. The sheep anti-Beta2-MG-HRPO conjugate is then added and reacted with the immobilized antigen for 30 minutes at 37 °C, resulting in the Beta2-MG molecules being sandwiched between the solid phase and enzyme-linked antibodies. The wells are washed with water to remove unbound-labeled antibodies. A solution of TMB is added and incubated for 20 minutes at room temperature, resulting in the development of a blue color. The color development is stopped with the addition of 1N HCl, changing the color to yellow. The concentration of Beta2-MG is directly proportional to the color intensity of the test sample. Absorbance is measured spectrophotometrically at 450nm.