It is becoming increasingly apparent that there exists an intimate bidirectional communication between the immune system and the nervous system. However, the field of 'neuroimmunology' has--for both mainstream immunologists and neuroscientists alike--often seemed more a realm of anecdotal, if not somewhat quirky, observations made by enthusiastic amateurs working at the fringes of each of the 'serious' mainstream disciplines. This perception is gradually changing as the detailed taxonomy of the immune system reveals that the component cells are equipped to respond to a plethora of soluble chemical messengers including serotonin, catecholamines, neurotrophins, opioids and several neuropeptides that, conventionally, have been considered as restricted to the neuroendocrine axis.