Alpha-2-macroglobulin (A2M) is a circulating 720 kDa homotetramer expressed in the liver which captures a wide range of plasma proteinases including plasmin and thrombin. Each monomer contains an internal thiol ester, a transglutaminase reactive site, zinc and receptor binding sites, and a bait region which when cleaved induces a conformational change trapping the proteinase. Serum A2M levels are decreased in acute pancreatitis and increased in chronic liver disease and nephrotic syndrome. The sensitive quantitative measurement of total human alpha-2-macroglobulin in samples is easily performed with this 96 well strip format ELISA kit. The normal human concentration of macroglobulin is 1.2 mg/ml in plasma. The assay measures total macroglobulin in the 1-250 ng/ml range. Samples giving human macroglobulin levels above 250 ng/ml should be diluted in blocking buffer before use. A 1:100,000 dilution for plasma is suggested for best results. Human macroglobulin will bind to the affinity purified capture antibody coated onto a micro titer plate. After appropriate washing steps, biotinylated primary antibody binds to the captured protein. Excess primary antibody is washed away and bound antibody is reacted with horseradish peroxidase conjugated streptavidin. Following an additional washing step, TMB substrate is used for color development at 450nm. Color development is directly proportional to the concentration of macroglobulin in the samples. A standard calibration curve is prepared using dilutions of purified macroglobulin and is measured along with the test samples. All reagents and standards are provided in these ELISA kits.