We analyzed the distribution of EMX1 during mouse development. EMX1 is a homeoprotein encoded by Emx1, a regulatory homeobox gene expressed in the developing forebrain. Its distribution essentially overlaps the expression domains of Emx1 transcripts. The EMX1 protein is present in the developing dorsa telencephalon, that is in the cerebral cortex, olfactory bulb and hippocampus. In the cerebral cortex EMX1 is present in nuclei of proliferating, differentiating and most mature neurons belonging to all cortical layers. In the olfactory bulb it is present in all proliferating cells during development, whereas postnatally it is faintly expressed in some mitral cells. Non-cerebral localizations include a transient expression in branchial pouches, in the apical ectodermal ridge of the developing limbs and in the developing kidney. Of particular interest is the presence of EMX1 in the olfactory nerve from its first appearance during embryogenesis to birth. The protein is present in axons of olfactory sensory neurons along their entire length, including their terminals in spherical regions of neuropil in the olfactory bulb called glomeruli.