Many methods exist for the assessment of membrane integrity, including several classic dye inclusion, exclusion and lysosomal accumulation techniques [7, 8] . Although well *Address correspondence to this author at the Research Department, Promega Corporation, 2800 Woods Hollow Road, Madison, WI, USA; E-mail: andrew.niles@promega.com validated, these methods are poorly suited for HTS implementation due to low sensitivity, multiple processing steps or miniaturization problems associated with higher plate densities [9, 10] . Recent advances in reagent formulations accommodate these miniaturized formats and are fully compatible with automated dispensing systems and integrated detection instruments. These reagents deliver the linearity, sensitivity, and robustness (Z' Values) necessary for properly interrogating large chemical libraries for cytotoxic risk. The most acceptable assay format is known as "add-mixmeasure", whereby reagent chemistry is delivered directly to the test well.