The morphology of the vomeronasal organ complex was histologically described in eight out of fourteen chiropteran species investigated. Of the six families examined, all except the family Pteropodidae (suborder Megachiroptera) were found to have at least one member possessing the organ. The organ is best developed in phyllostomatids. It is absent in vespertilionids (including a Myotis embryo) except in Miniopterus. An accessory olfactory bulb is reported for the first time in the latter. The organ is described for the first time in Rhinopoma, Megaderma, and Hipposideros. The organ in Rhinolophus is also described. Homologous anterior nasal cartilages and patent nasopalatine ducts are present in all species. The organ occupies the anterior ventral nasal septum region. In Megaderma and Hipposideros it is level with the nasal cavity floor. Areas of epithelium similar to olfactory epithelium have been observed in some organs. Epithelia, vascular sinuses, vomeronasal nerves, paravomeronasal ganglia, accessory olfactory bulbs, and vomeronasal glands have been investigated. In bats with regressed or rudimentary organs (Megaderma, Rhinopoma, Rhinolophus, Hipposideros) accessory olfactory bulbs could not be identified. Thus, presence of the organ does not necessarily indicate presence of the accessory olfactory bulb. Septal pockets located superior to the organ complex and lined with pseudostratified columnar epithelium are described in Hipposideros and may play a part in nasophonation. A unique role is proposed for the organ in the feeding behaviour of Desmodus. The desirability of extending the useful terms 'diosmatic' and 'monosmatic' to all vertebrates in reference to their respective possession or lack of the vomeronasal organ is suggested.