The Fura-2 QBT Calcium kit combines the calcium indicator Fura-2 with masking technology to provide a ratiometric fluorescence-based assay for detecting and quantitating changes in intracellular calcium. The kit is designed to reduce background fluorescence in media around cells, enabling researchers to more easily detect signals from within the cell. Also, the kit eliminates the need for wash protocols. The Fura-2 dye is excited at two different wavelengths, enabling ratiometric measurement of calcium flux to reduce the impact of assay variances caused by uneven dye loading, leakage, or cell density. The kit is validated for use on FlexStation 3 and FLIPR Tetra systems.