CMV Ab IgM fast is an one-step sandwich assay based on micro wells coated with recombin ant antigens of Cytomegalo virus (rAg). The conjugate is a mixture of HRP-labeled polyclonal anti-human-IgM antibodies (mAb). Serum samples are added to the wells and if anti-Cytomegalo virus antibodies are present in a sample, they form stable complexes with antigens immobilized on the wells. Then the antigen-antibody complexes are identified by the addition of HRP labeled anti-human- IgM conjugate. The unbound components are removed by washing. After addition of the solution containing TMB and hydrogen peroxide, the wells with bound conjugate develop a blue colour which is converted to yellow after the reaction has been stopped with sulphuric acid. The colour intensity is directly proportional to the concentration of IgM antibodies to Cytomega- lovirus in the specimen and can be read at 450 nm.