MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium), in the presence of phenazine methosulfate (PMS), produces a formazan product that has an absorbance maximum at 490 nm in phosphate-buffered saline. The MTS assay is often described as a 'one-step' MTT assay, which offers the convenience of adding the reagent straight to the cell culture without the intermittent steps required in the MTT assay. However this convenience makes the MTS assay susceptible to colormetric interference as the intermittent steps in the MTT assay remove traces of coloured compounds, whilst these remain in the microtitre plate in the one-step MTS assay.