The degree of topographical organization of epithelium-to-bulb connections in 15-day-old rats was analyzed from the complete mapping of these projections previously described by using the HRP retrograde tracing method. We performed HRP placements in the antero-posterior (anterior, central and posterior injections) and dorso-ventral bulbar axes. Results demonstrated: lack of transposition of any plane of the epithelial sheet along the antero-posterior axis in the bulb which indicated a typical diffuse distribution of projections along this bulbar plane; a general tendency of the medial, lateral, dorsal and ventral epithelial regions to project to homologous bulbar surfaces; however, this transposition was always relative; the importance of the dorso-ventral bulbar axis in the somatotopic organization of projections since this plane was a common plane on which the different mucosal axes were represented. These results suggest that the topographical organization of projections reflects the ontogenetically determined epithelium-to-bulb connections.