Purified CMV antigen is coated on the surface of microwells. Diluted patient serum is added to the wells, and the CMV IgM specific antibody, if present, binds to the antigen. All unbound materials are washed away. HRP-conjugate is added, which binds to the antibody-antigen complex. Excess HRP-conjugate is washed off and a solution of TMB Reagent is added. The enzyme conjugate catalytic reaction is stopped at a specific time. The intensity of the color generated is proportional to the amount of IgM specific-antibody in the sample. The results are read by a microwell reader compared in a parallel manner with calibrator and controls.