Senescent cells show common biochemical markers such as expression of an acidic senescence-associated ß-galactosidase (SA-ß-Gal) activity. While senescence has been characterized primarily in cultured cells, there is also evidence that it occurs in vivo. Cells expressing SA-ß-Gal have been identified in normal tissues. Cell Biolabs' Quantitative Cellular Senescence Assay Kit uses a non-toxic fluorogenic substrate to measure SA-ß-Gal activity. This compound is a membrane permeable, non-fluorescent substrate of ß-galactosidase, which after hydrolysis of the galactosyl residues emits green fluorescence and remains confined within the cell. In comparison to the conventional cytochemical assay using X-gal, the use of a the fluorogenic substrate greatly enhances the sensitivity of the assay and allows you to study living cells by flow cytometry for more quantitative measurement of SA-ß-Gal activity. Each kit provides sufficient quantities to perform up to 10 assays in 35 mm wells.