The GSH/GSSG-Glo™ Assay is a luminescence-based system that detects and quantifies total glutathione (GSH + GSSG), GSSG and GSH-to-GSSG ratios in cultured cells. Reduced glutathione (GSH) and oxidized glutathione (GSSG) both exist in healthy cells, the majority of which is in reduced (GSH) form. A change in GSH and GSSG levels are important when assessing toxicological responses and an indicator of oxidative stress, potentially leading to apoptosis or cell death. The GSH and GSSG detection assay provides a simple, rapid multiwell-plate format where stable luminescent signals are correlated with either the total GSH or the GSSG concentration of a sample directly in culture wells. The simple sample processing and stable signal make the assay amenable to high-throughput analysis.