The microtiter plate provided in this kit has been pre-coated with an antibody specific to TSH. Standards or samples are then added to the appropriate microtiter plate wells with a Horseradish Peroxidase (HRP)-conjugated antibody preparation specific for TSH and incubated. Then substrate solution A and B are added to each well. Only those wells that contain TSH, HRP-conjugated antibody will exhibit a change in color. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid