Chemosensory systems in the mammalian nasal cavity are said to be functional before birth. Fluorescent beads (1 micron, diameter), injected into the amniotic fluid surrounding E18 mouse fetuses, were sought in serial frozen sections of E19 animals. Beads were found in all regions of the nasal cavity except for the lumen of the vomeronasal organ (VNO) where the receptor neurons of the accessory olfactory system (AOS) are located. Thin plastic sections through the rostral aspect of the E19 nasal cavity revealed that the VNO canals, which provide stimulus access to the AOS, are not patent. Thus, this chemosensory system can be excluded as a potential channel of chemosensory information for the mouse fetus.