Although many assay methods have been developed for determining cytotoxicity in lower density formats, precious few have been validated for use in high throughput screening that requires simple, homogenous assay procedure with robust assay signal. Niles et al. recently described a novel proteolytic biomarker profile for cytotoxicity that embodies many biological attributes desirable for robust assay development (Niles et al., 2007). Subsequently, a homogenous luminescent assay was developed for measuring this biomarker that comprises a formulation containing an aminoluciferin-conjugated substrate, ATP, MgSO4 and a thermostable, recombinant luciferase (Figure 1). We describe here the development and validation of a bioluminescent cytotoxicity assay using a protease biomarker in a 1536-well plate format, by the screening of the1408 compound collection from National Toxicology Program (NTP) (Xia et al., 2008). We have identified several known and novel membrane disrupters by screening NTP library, which indicates that the assay is robust and suitable for large scale library screening.