Investigation into the nature and mechanism of action of neurotrophins dates back to the description of a “nerve growth factor” activity by Levi-Montalcini (described inrefs. 1 and 2) and has progressed to include a family of factors, several of which have been assessed in Federal Drug Administration (FDA) trials to treat neurodegenerative diseases. Study of neurotrophins and their receptors has employed many paradigms, including knockout animals, primary neuronal cultures, and a variety of cell lines. Perhaps the most popular of the cell lines used in these investigations is the rat pheochromocytoma cell line PC 12 (3). PC 12 cells resemble immature adrenal chromaffin cells until stimulated to differentiate into a sympathetic neuronlike state by nerve growth factor (NGF) treatment. The documented similarities between neuronally differentiated PC 12 cells and cultured neurons, at both the morphological and biochemical levels, are striking and have underscored the utility of the PC 12 cell system in neurotrophin research (reviewed in refs. 4–6).