Q-VD-OPh is a broad spectrum caspase inhibitor that provides a cost effective, non toxic, and highly speci?c means of apoptotic inhibition and provides new insight into the design of new inhibitors. It is more stable in aqueous environments and exhibits several folds higher activity than the widely used inhibitors, ZVAD-FMK and Boc-D-FMK. Q-VD-OPh is also equally effective in preventing apoptosis mediated by the three major apoptotic pathways, caspase 9/3, caspase 8/10, and caspase 12. It can inhibit recombinant caspases 1, 3, 8, and 9 with IC50 values ranging from 25 to 400 nM, and has been shown to strongly inhibit caspases 7, 10, and 12 at higher concentrations (10 µM). Q-VD-OPh protected against the substantial apoptosis induced by actinomycin D. In addition, Q-VD-OPh alone exhibits little or no toxicity, even at extremely high concentrations.