The vomeronasal organ was studied in mature dogs with the optical, transmission electron, and scanning electron microscopes. The canine vomeronasal complex is structurally well developed. Large blood vessels are present deep to both the lateral, 'non-receptor' and medial, 'receptor' epithelia. In addition to the unmyelinated vomeronasal nerves in the lamina propria deep to the 'receptor' epithelium, numerous nerves containing both myelinated and unmyelinated fibres are present deep to the 'non-receptor' epithelium. The 'non-receptor' epithelium consists of basal cells, ciliated and non-ciliated columnar cells, and globular cells packed with mitochondria. Contained within the 'non-receptor' epithelium are leucocytes, plasma cells, and nerve endings. The 'receptor' epithelium consists of basal, sustentacular, and ciliated receptor cells. The microtubules in cilia of the receptor cells do not appear to have dynein arms or radial spokes.