We investigated neuronal cell differentiation, particularly neurite outgrowth, on the surface of diX H and diX AM using an in vitro examination of a neuron-like rat pheochromocytoma cell line, PC12. diX H and diX AM are in the parylene family of diX C (or Parylene-C), which is widely used as a novel coating material to insulate neural electrodes, and they have been recently commercialized; diX H and diX AM offer different features of biocompatibility. Previously, we found that these new parylene materials have high cell adhesiveness to neuronal cells whereas the adhesiveness of diX C is extremely low. However, their cell differentiation remains unknown although neuronal cell differentiation plays a crucial role in their development and regeneration. This study showed that almost all PC12 cells adhering to the surface of diX AM and diX H were differentiated, but the neurite outgrowth was significantly larger on diX H than that on diX AM and a conventional polystyrene culture dish. The result suggests that diX H may be advantageous as a biocompatible coating material for a scaffold, which can be used on virtually any substrate to get various configurations in neural devices. (c) 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2012