One of the most striking features of neurons in the mature peripheral nervous system is their ability to survive and to regenerate their axons following axonal injury. To perform a comprehensive survey of the molecular mechanisms that underlie peripheral nerve regeneration, we analyzed a cDNA library derived from the distal stumps of post-injured sciatic nerve which was enriched in non-myelinating Schwann cells using cDNA microarrays. The number of up-and down-regulated genes in the transected sciatic nerve was 370 and 157, respectively, of the 9596 spotted genes. In the up-regulated group, the number of known genes was 216 and the number of expressed sequence tag (EST) sequences was 154. In the down-regulated group, the number of known genes was 103 and that of EST sequences was 54. We obtained several genes that were previously reported to be involved in regeneration of the injured neurons, such as cathepsin D, ninjurin 1, tenascin C, and co-receptor for glial cell line-derived neurotrophic factor family of trophic factors. In addition to unknown genes, there seemed to be a lot of annotated genes whose role in nerve regeneration remains unknown. Keywords: cDNA microarrays, injury-induced molecules, nerve regeneration, Schwann cell, sciatic nerve. One of the most striking features of neurons in the mature PNS is their ability to survive and to regenerate their axons following axonal injury. It has been increasingly evident that the success of axonal regeneration is dependent on the intrinsic as well as extrinsic growth properties of the axotomized neuron. The environment in which PNS axons regenerate consists of Schwann cells and their basal laminae, fibroblasts, collagen, degenerating myelin and phagocytic cells (Fawcett and Keynes 1990;Bunge and Griffin 1992;Araki and Milbrandt 1996). After nerve injury, the distal axonal and myelin segment undergoes dissolution and absorption by the surrounding cellular environment, a process called Wallerian degeneration. Then, the remaining Schwann cells divide and align longitudinally within basal lamina tubes. Growth cones from regenerating axons extend along the Schwann cell bands (the band of Bü ngner), growing along the Schwann cell membranes and basal laminae (Keynes 1987;Reichert et al. 1994;Grill and Tuszynske 1999). Such biological and morphological changes of Schwann cells are thought to be controlled by injury-induced molecules that are expressed by neurons and Schwann cells themselves. Especially, at around 7 days after nerve injury, many nerve regeneration-related factors, such as p75 NTR , co-receptor for glial cell line-derived neurotrophic factor family of trophic factors (GFRa1) and ninjurin 1 and 2, reach peak levels (Taniuchi et al. 1988;Araki and Milbrandt 1996;Baloh et al. 1997;Araki and Milbrandt 2000), and the growth cones of regenerating axons begin to move over the Schwann cell surface (Taniuchi et al. 1988;Goodrum et al. 1994). Successive large-scale screening, however, is required to reveal the spectrum of genes involved in this regenerat...