ABSTRACT: Recent publications show that the human vomeronasal organ (VNO) develops and grows during gestation, and is present in all adult humans. The human VNO has a unique ultrastructure, with elongated bipolar microvillar cells that stain with several immunomarkers. These cells show physiological properties similar to chemosensory receptor cells of other mammalian species. The adult human VNO displays species-specific, gender-dimorphic and highly stereospecific responses to ligands. The organ's local response, or electrovomerogram, is followed by gender-specific behavioral changes, modulation of autonomic nervous system function, or the release of gonadotropins from the pituitary gland. Functional brain imaging studies revealed consistent activation of the hypothalamus, amygdala and cingulate gyrus-related structures during adult human VNO stimulation. These findings present new information supportive of a functional vomeronasal system in adult humans.