The field of neurotrophic factors has witnessed exp- sive growth in the past decade. As is usual in scientific in- vation, this progress has been closely associated with methodological advances. The introduction of molecular b- logical techniques into the neurotrophic factor field led to the discovery of new families of neurotrophic growth f- tors and their receptors. Production of growth factors by recombinant technology played a crucial part. The example of nerve growth factor, the paradigmatic neurotrophic factor, illustrates this point. A decade ago investigators were forced to purify small quantities of this protein from murine salivary glands, but much larger qu- tities of recombinant nerve growth factor are now available for experimentation as well as clinical development. A decade ago there was a controversy about the existence of nerve growth factor in the brain and the immunoassays used for its measurement, but current publications report the precise localization of gene expression for nerve growth factor and its receptor in the brain. Neurotrophic Factors aims at presenting the techniques that have been crucial to the realization of these rapid advances and thus have helped propel the neurotrophic factors field to its current status of high visibility. These techniques range from molecular biological methods used for cloning and production, to cell culture methods for assessing biological activities, to animal models of nervous system injury (nec- sary for the development of therapeutic agents from neurotrophic factors).