Methods for assessing mammalian cell death are presented in this unit. The unit is divided into six sections: (1) a brief overview of cytotoxicity and pathways of cell death, (2) a method to measure cell death using lactate dehydrogenase (LDH) release as a marker of membrane integrity, (3) a flow cytometry method that simultaneously measures two types of cell death, necrosis, and apoptosis, (4) use of fluorescence microscopy and nuclear morphology to assess apoptosis and necrosis, (5) the use of multi-well plates and high-content analysis imaging systems to assess nuclear morphology, and (6) a discussion of the use of cytotoxicity assays to determine the mechanisms of cell death.