Schwann cells, expanded in number by exposure to growth factors in vitro, could be useful in nervous system repair. Our previous results suggest that long term exposure to heregulin and forskolin changes the functional properties of the human Schwann cells, including the ability to myelinate axons after transplantation. Here, we propose to determine the molecular changes in the Schwann cells that occur as a result of extended growth with mitogenic factors. We believe that the information obtained in these studies will provide clues about mechanisms underlying the already observed changes in function. This information will aid in the prediction of the safety and efficacy of neural repair approaches that use cultured, expanded Schwann cells. Finally this data may provide clues into the mechanisms underlying normal human Schwann cell function.