The initial event in olfactory perception is the binding of odorant molecules to specific receptor proteins in the human nose. The interaction between odorant and receptor initiates olfactory signal transduction that leads to a cation influx and change in the membrane potential of the olfactory sensory neuron. In this study, a microfabricated planar electrode was used to measure the generated membrane potential in a heterologous olfactory system. Human embryonic kidney (HEK)-293 cells expressing the olfactory receptor I7 were transfected with the gustatory cyclic nucleotide gated (CNG) channel to amplify the membrane potential. A microfabricated planar electrode was used to measure the electrical responses of odorant-receptor binding. Stimulation of the olfactory receptor with its specific odorant caused an intracellular Ca(2+) influx, which was quantitatively measured using a planar electrode. The extracellular field potential generated by the Ca(2+) influx through the CNGgust channel of the cells was approximately 10 mV. This cell-based olfactory biosensor, which uses a microfabricated planar electrode for detection, would be useful for screening specific ligands for binding to orphan olfactory receptors.