Transplantation of olfactory ensheathing cells has been one of the promising strategies in enhancing central nerve fiber regeneration. Membrane surface molecules on olfactory ensheathing cells mediating cell-cell interactions as well as various factors released from them are thought to be important for nerve regeneration. The latter, however, has not been fully substantiated by experimental data, particularly regarding the olfactory ensheathing cells of the adult animals. In the present study, the effects of adult olfactory ensheathing cell conditioned medium on PC12 cells were examined. The results show that the factors secreted by the adult olfactory ensheathing cells can promote PC12 cell differentiation and protect it from Zn(2+) insult.