Immunoglobulin M (IgM) is the first immunoglobulin produced in the immune response and is the third most abundant immunoglobulin in serum. IgM is a disulfide-linked 970kDa pentamer that activates complement and is responsible for red blood cell agglutination. Each monomer consists of two mu heavy chains and two kappa or lambda light chains. The sensitive quantitative measurement of total human IgM antigen in serum, plasma, hybridoma cell supernatants, ascites or other biological fluid samples is easily performed with this 96 well strip format ELISA kit. The concentration of IgM in normal human serum ranges from 0.5 to 2.0 mg/ml. The assay measures human IgM in the 0.2-200 ng/ml range. Samples giving human IgM levels above 200 ng/ml should be diluted in blocking buffer before use. A 1:25,000 to 1:200,000 dilution for normal human serum or plasma is suggested for best results. Human IgM will bind to the affinity purified capture antibody coated on the microtiter plate. After appropriate washing steps, peroxidase labeled anti-human IgM primary antibody binds to the captured protein. Excess antibody is washed away and TMB substrate is used for color development at 450nm. Color development is proportional to the concentration of human IgM in the samples. A standard calibration curve is prepared in blocking buffer using dilutions of purified human IgM and is measured along with the test samples. All reagents and standards are provided in these ELISA kits.