The number of vomeronasal receptor cells and olfactory receptor cells were determined in several turtles and tortoises. Using semi-aquatic turtles with developed vomeronasal organs, neural responses to various odor stimuli were recorded as extracellular unitary spike responses of vomeronasal receptor cells, compound action potentials from vomeronasal nerve twigs, induced wave responses on the accessory olfactory bulb (AOB) surface and unitary responses of AOB neurons. The vomeronasal system in turtles responded to various volatile and non-volatile chemicals. These results yield insights concerning functions of the vomeronasal organ in semi-aquatic turtles.