The CellTiter-Glo 2.0 Assay provides a homogeneous method for determining the number of viable cells in culture by measuring the amount of ATP present, which indicates the presence of metabolically active cells. The CellTiter-Glo 2.0 Assay is based on the original CellTiter-Glo Assay chemistry but with improved storage convenience for easy implementation. The CellTiter-Glo 2.0 Assay is provided as a single, ready-to-use reagent that can be stored at 4C for up to 2 months with >85% activity remaining or at room temperature for 1 week with >85% activity remaining. The CellTiter-Glo 2.0 Assay is designed for use with multiwell plate formats, making it ideal for automated high-throughput screening (HTS), cell proliferation and cytotoxicity assays. The homogeneous assay procedure involves adding the single reagent (CellTiter-Glo 2.0 Reagent) directly to cells cultured in serum-supplemented medium. Cell washing, removal of medium and multiple pipetting steps are not required. The system detects as few as 15 cells/well in a 384-well format in 10 minutes after adding reagent. The homogeneous "add-mix-measure" format results in cell lysis and generation of a luminescent signal proportional to the amount of ATP present. The amount of ATP is directly proportional to the number of cells present in culture. The CellTiter-Glo 2.0 Assay generates a "glow-type" luminescent signal, which has a half-life generally greater than three hours, depending on cell type and medium used. The extended half-life eliminates the need to use reagent injectors and provides flexibility for continuous or batch-mode processing of multiple plates.