N-Pentafluorobenzoyl-R110 (1a) and N-(2,3,4,5-tetrafluorobenzoyl)-R110 (1b) with enhanced cell retention properties, were prepared from rhodamine 110 (R-110) and the corresponding polyfluorobenzoyl chloride. N-Ac-DEVD-N'-pentafluorobenzoyl-R110 (3a) and N-Ac-DEVD-N'-(2,3,4,5-tetrafluorobenzoyl)-R110 (3b) were prepared as tetrapeptide substrates for caspases. Substrate 3b was efficiently cleaved by human recombinant caspase-3 in an enzyme assay. Substrate 3b also was efficiently cleaved in cell-based apoptosis assays. After cleavage in apoptotic cells by activated caspases, the substrate becomes fluorescent as measured by flow cytometry. These substrates should prove useful in cell-based assays for studying apoptosis inducers and inhibitors.