CellCountEZ? Cell Survival Assay Kit is a tissue culture media-based assay that can measure metabolically active live cells and quantify cell death caused by radiation, chemotherapeutics or toxins. CellCountEZ? is based on the ability of mammalian cells to rapidly and efficiently convert hydroxyethyl disulfide (HEDS) into mercaptoethanol (ME) through a bioreduction mechanism. Bioconversion of HEDS to ME relies on the activity of the oxidative pentose phosphate cycle (OPPC). CellCountEZ? measures ME in the extracellular medium without the need for cellular lysis and extraction methods, this preserves the ability to perform other cellular tests in the same culture system. CellCountEZ? is readily soluble, membrane permeable and converted by live cells intracellularly before transport into the extracellular culture media. CellCountEZ? offers many advantages that make it superior to common existing methods for quantifying cell growth and survival. Synonyms: Toxicity, Proliferation, and Survival Assay, cell proliferation and survival, drug screening, cell viability, cell survival, cellular viability, cellular survival, HEDS assay.