Objectives/Hypothesis: To functionally investigate the distribution of the olfactory epithelium in humans by means of the electro-olfactogram (EOG) and anatomically located biopsy specimens. Study Design: Prospective, nonrandomized, investigational. Methods: Supra-threshold EOG recordings were made on 12 healthy, trained volunteers (6 women, 6 men; age range, 21-48 y), Vanillin was used as the stimulus, since it exclusively excites olfactory receptor neurons. The EOG was recorded with tubular electrodes that were placed using thin-fiber endoscopic guidance. Biopsy specimens were obtained of anterosuperior nasal cavity mucosa in the same regions as the positive EOGs in 15 smell-tested patients (7 women, 8 men; age range, 22-60 y) during routine nasal and sinus surgery. This biopsied tissue was histologically processed and stained for olfactory and neural proteins. Results: Viable responses to EOG testing were obtained in 7 of 12 subjects. In these seven subjects it was possible to identify nine sites above or below the anterior middle turbinate insertion where EOGs were obtained. The biopsy results showed mature olfactory receptor neurons in this same area. Conclusions: Human olfactory epithelium appears to be distributed more anteriorly than previously assumed.