Screening technologies for G protein-coupled receptors comprise two major approaches; homogeneous assays, conducted in microtiter plate formats, and protein redistribution assays that require imaged-based analysis using automated confocal systems. Generally, the former are used in primary screening campaigns for lead identification, while the latter are used in secondary screens for lead optimization. Homogeneous assays measure changes in G protein-coupled receptor second messengers such as cAMP, Ins P3 or calcium. Protein redistribution assays assess internalization of the receptor ligand complex or translocation of G-protein coupled receptor-associated proteins, such as beta-arrestin. In the present review functional cell based approaches are discussed, emphasizing the variety of non radiometric technologies now in use for HTS.