Glutathione (GSH) is a low molecular-weight tripeptide thiol that serves as a primary cellular anti-oxidant and plays a fundamental role in the elimination of environmental toxins. During early apoptosis, cells may exclude GSH, causing a decrease in intracellular GSH levels. The intracellular level of GSH is thus used as an indicator of cell health. Cayman’s Cell-Based Glutathione Assay Kit (Blue Fluorescence) employs a cell-permeable dye, monochlorobimane (MCB), which reacts with GSH to generate a highly fluorescent product that can be measured using excitation and emission wavelengths of 380 and 480 nm, respectively. The kit can be easily adapted to screening programs for therapeutic compounds regulating intracellular GSH levels.