These cell-based, no-wash kits were developed for Molecular Devices' FLIPR® and FlexStation® systems for GPCR screening and assay development. To address the challenging requirements of an expanding number of GPCRs and ligands, Molecular Devices introduces the FLIPR Calcium 4 Assay Kit. This new kit utilizes a novel masking dye technology which is exclusively licensed to Molecular Devices from Bayer AG (patent nos. US 6,420,183, EP 0906572). The masking technology significantly lowers background fluorescence and improves signal-to-noise without washing the cells.