TBD DNA Damage (ATM) and Cell Cycle Analysis Kit is designed to identify the linkage between DNA damage in relation to cell cycle checkpoints in flow ytometry applications. The kit includes a directly conjugated Anti-phospho-ATM (Ser1981) Alexa Fluor® 488 conjugate plus a DNA dye (Propidium Iodide) which allows the researcher to perform bivariate analysis to identify where DNA damage takes place relative to the positioning within the cell cycle. The kit includes an optimized protocol with all of the necessary components to provide the researcher a true “plug and play” design for their research when studying DNA damage and cell cycle checkpoints. This immunocytochemical method is very sensitive, and additionally it offers the capability to screen antitumor drugs at every phase of the cell cycle.