Repairing the diseased or injured nervous system remains one of the greatest challenges for medical science. The problem can be approached from several directions. For example, we can encourage the nervous system to repair itself by providing it with trophic factors, or we can transplant stem cells to replace the lost tissue. Both of these approaches are considered in reviews in this issue. Airaksinen and Saarma (page 383) discuss the how glial cell line-derived family of neurotrophic factors might be used to treat a variety of neurological disorders. Rossi and Cattaneo (page 401), on the other hand, cast a critical eye over progress that has been made towards the use of stem cells to repair the central nervous system. The latter has been the subject of intense media attention over the past few years, and some extravagant claims have been made about the properties of stem cells and their therapeutic potential, not all of which have yet been substantiated. Rossi and Cattaneo consider what steps need to be taken to ensure that we can exploit stem cells to the full, and argue for a more integrated approach that takes into account the specific problems that are posed by different disease mechanisms.

The field of stem cell research received a significant boost recently, when it was announced that researchers in the UK are to be allowed to clone human embryos to derive embryonic stem cell lines. Of course, at this stage, it is important that we keep our feet on the ground, and do not jeopardize our credibility by professing a miracle cure. However, the development of these cell lines will undoubtedly help us to learn more about the properties of stem cells and how to control their differentiation to achieve the desired results.