A review. Cell-based assays are the predominant means of assessing activation of ionotropic receptors and G protein-coupled receptors (GPCRs), but are limited by their inherent complexity. Here we present an approach to immobilize receptors stably and with defined orientation in microarrays on sensor surfaces. Using optical and elec. methods we were able to follow ligand binding, receptor activation and receptor deactivation. Our findings are a novel approach for functional screening of pharmacol. interesting receptor proteins in high d. format. [on SciFinder (R)]