Abstract : Extracellular microelectrode recordings were made from single neurons of the olfactory bulb in anesthetized tracheotomized rats. Air, oxygen, argon, and nitrogen were perfused through the nasal cavities in order to determine whether the response of olfactory bulb neurons to x-rays was dependent on the particular gas present within the nasal cavities. Head-only x-irradiation (250 KVP, 100 R/minute) produced responses in many neurons during the perfusion of all four gases used. Such responses were ordinarily depressed, however, during argon or nitrogen perfusion as compared with the responses obtained during air or oxygen perfusion. In some cases, argon and nitrogen abolished the response to radiation within 5 minutes. It was concluded that the response of olfactory bulb neurons to x-rays was not dependent on the presence within the nasal cavities of any of the gases used. It was also concluded that the response of olfactory bulb neurons to x-irradiation depends upon an effect on olfactory receptors, since the response could be modified in most cases by the perfusion of argon and nitrogen. (Author)