Glutathione (GSH) is involved in maintenance of protein sulfhydryl reduction status. PSSG may modify the activity of a large number of cell proteins, including metabolic, structural, cytoskeletal, and signaling proteins. Cayman’s PSSG provides a convenient method for the direct visualization of S-glutathionylated proteins in whole (permeabilized) cells by flow cytometry and microscopy as well as avidin overlay analysis. This cell-based assay starts with the modification of protein free-thiols groups followed by enzymatic cleavage of any PSSG adducts present in the sample. Biotinylation of the newly-formed protein free-thiols provides the basis for visualization using streptavidin-based colorimetric or fluorescence detection. Reagents are provided to test three sets of 10 samples (most convenient) or up to thirty samples total at once if desired.