Activation of G-protein coupled receptors (GPCR) that couple to Gαθ and Gβγ and subsequent activation of phospholipase C –β (PLC-β) can be detected through the measurement of D-myo-inositol 1,4,5-triphosphate (IP3) in cells. This chapter describes technologies that can be used to develop robust assays for screening compounds, more specifically the use of Homogeneous Time-Resolved Fluorescence Assay (HTRF) for IP3 measurement. A sample preparation protocol, parameters for assay optimization and examples of data analysis are provided.