Biosensors based on isolated receptors, together with planar bilayer lipid membranes (BLMs), provide a highly sensitive and selective sensing method for bioactive substances. Although isolation of receptors from mammals is necessary for designing the sensors, the sensors are easily fabricated, if adequate procedures for isolation of receptor proteins and formation of receptor-incorporated BLMs are made. This chapter describes two examples of biosensors based on isolated receptors: glutamate receptor ion channels (GluRs) that induce membrane permeability changes on binding l-glutamate, and a Na⁺/d-glucose cotransporter that displays active transport of d-glucose.