The microtiter plate provided in this kit has been pre-coated with Mouse IgA. Samples are then added to the appropriate microtiter plate wells with a Horseradish Peroxidase (HRP)-conjugated antibody preparation specific for Mouse IgA and incubated. Then substrate solutions are added to each well. Only those wells that contain Mouse IgA and enzyme-conjugated Mouse IgA will exhibit a change in color. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid solution and the color change is measured spectrophotometrically at a wavelength of 450 nm ± 2 nm.