The past decade has seen a number of significant changes in identifying higher quality lead compounds earlier in the drug discovery process. Cell-based assay technologies yielding high-content information have emerged to achieve this goal. Although most of these systems are based on fluorescence detection, this article describes the development and application of an innovative cellular assay technology based on radio frequency spectrometry and bioimpedance measurements. Using this technique, the authors have discovered a link between cellular bioimpedance changes and receptor-mediated signal transduction events. By performing dielectric spectroscopy of cells across as pectrum of frequencies (1 KHz to 110 MHz), a series of receptor-specific, frequency-dependent impedance patterns is collected. These raw data patterns are used to determine the identity of the cellular receptor-signaling pathway being tested and to quantify stimulation endpoints and kinetics. The authors describe the application of this technology to the analysis of ligand-induced cellular responses mediated by the 3 major classes of G-protein-coupled receptors (GPCRs) and protein tyrosine kinase receptors. This single assay platform can be used with ease to monitor G(s), G(i), and G(q) GPCRs without the need for chimeric or promiscuous G-proteins, fluorophors, or tagged proteins. In contrast to other methods of monitoring cellular signal transduction, this approach provides high information content in a simplified, noninvasive, and biologically relevant fashion.