Olfactory ensheathing cells (OECs) migrate from the olfactory epithelium towards the olfactory bulb during development.However, the guidance mechanism for OEC migration remains a mystery.Here we show that migrating OECs expressed the receptor of the repulsive guidance factor Slit-2.A gradient of Slit-2 in front of cultured OECs first caused the collapse of the leading front, then the reversal of cell migration.These Slit-2 effects depended on the Ca2+ release from internal stores through IP3 receptor channels.