Fully-luminescent formats are highly desirable for HTS environments because of the aforementioned advantages over fluorescent methods. Another remarkable feature of luminogenic assays is the persistent and stable glow-type signal produced after reagent addition (Fig. 8) . This attribute can be harnessed to produce both viability and cytotoxicity values from the same well. In this method, the non-lytic, luminogenic cytotoxicity assay chemistry is first delivered to the assay well and cytotoxicity measured. Next, a lytic agent is added to assay wells to artificially release the remaining dead cell protease from viable cells. The net signal derived after complete lysis reflects the contribution of all the cells in the assay well. Because the luminescent signal is additive and proportional, the viable cell population can be indirectly determined by subtracting the cytotoxic values from the total values. This method is particularly useful for determining cytotoxicity in long incubation protocols where dead cell biomarker activity may not fully reflect actual cytotoxicity. One caveat of this method is that both viability and cytotoxicity measurements utilize the same biomarker and are subject to the same interferences.