Activation of members of caspase-family proteases plays a key role in apoptosis. The CaspSCREENTM Flow Cytometric Apoptosis Detection Kit provides a convenient means for detecting activation of caspases by flow cytometry in living cells. The assay is based on the cleavage of (aspartyl)2-Rhodamine 110 (D?R), a reported substrate for members of caspase family proteases. The caspase substrate D?R is non-fluorescent, however, upon cleavage of the substrate by cellular caspases, the released rhodamine 110 gives rise to fluorescence that can be measured at excitation of 488 nm and emission of 530 nm.