This ELISA kit uses the Competitive-ELISA principle. The micro ELISA plate provided in this kit has been pre-coated with GSH. During the reaction, GSH in samples or Standard competes with a fixed amount of GSH on the solid phase supporter for sites on the Biotinylated Detection Ab specific to GSH. Excess conjugate and unbound sample or standard are washed from the plate, and Avidin conjugated to Horseradish Peroxidase (HRP) are added to each microplate well and incubated. Then a TMB substrate solution is added to each well. The enzyme-substrate reaction is terminated by the addition of stop solution and the color change is measured spectrophotometrically at a wavelength of 450 ± 2 nm. The concentration of GSH in the samples is then determined by comparing the OD of the samples to the standard curve.