The expression of 9-O-acetylated gangliosides recognized by the Jones monoclonal antibody (mAb) correlates with cell migration and axonal outgrowth in the developing rat nervous system. We studied the expression of these gangliosides during the development and maturation of the rat olfactory system. Beginning on embryonic day 13 (E13) the olfactory epithelium and the migratory mass were intensely stained with Jones mAb. However, though this immunoreactivity disappeared from the olfactory epithelium at E19, it remained in a few fascicles and some glomeruli of the newborn and adult olfactory bulbs. We concluded that the expression of 9-O-acetylated gangliosides by olfactory axons and/or migrating cells may facilitate axonal outgrowth during development and might be involved in the formation of new glomeruli in the mature olfactory bulb.