Our Cell Meter™ assay kits are a set of tools for monitoring cell viability. There are a variety of parameters that can be used for monitoring cell viability. This particular kit is designed to monitor cell apoptosis through measuring the depleted antioxidant reduced glutathione (GSH). GSH is involved in many cellular processes including the scavenging of free radicals, drug detoxification, cell signaling, and cell proliferation. The decrease in cellular GSH concentration is an early hallmark in the progression of cell death in response to different apoptotic stimuli in many cell types. Our Cell Meter™ Intracellular GSH Assay Kit provides all the essential components with an optimized assay method for the detection of apoptosis in cells with the decreased GSH. This fluorometric assay is based on the detection of the GSH in cells using our proprietary non-fluorescent Thiolite™ Green dye that becomes strongly fluorescent upon reacting with thiol. In normal cells, Thiolite™ Green accumulates primarily in cytosol, but it is partially translocated to mitochondria in apoptotic cells while Thiolite™ Green staining intensity decreases. Cells stained with Thiolite™ Green can be visualized by flow cytometry with Ex/Em = 490 nm/520 nm (FL1 channel). The kit can be paired with other reagents, such as 7-AAD (Cat# 17501), propidium iodide (Cat# 17517) for multi-parametric study of cell viability and apoptosis. The kit is optimized for screening of apoptosis activators and inhibitors by flow cytometry.