Over the last decade, a considerable wealth of information has expanded and strengthened our knowledge of the relations between the nervous, endocrine, and immune systems. The following areas of progress may be underlined 1) the cells of the three systems appear to secrete similar substances and are sensitive to them, thus suppressing traditional differences between neurotransmitters, hormones and immune mediators; 2) new knowledge is available on hormone actions on the immune system, and direct and mutual influences between the nervous and the immune system have been documented; 3) brain areas selectively involved in immune regulation have been identified; 4) various brain functions are now known to be influenced by immune mediators; 5) neurological and psychiatric components have been described in autoimmune diseases. An immune etiology has been unraveled in a wide range of neural disorders. A neuroimmunological component has been documented in a growing number of diseases. Altogether, a new chapter is emerging in our understanding of homeostatic functions and their medical implications.