The study of neurotransmitters in the human brain has expanded spectacularly in recent years with the application of techniques from immunology and molecular biology. These techniques are now being used successfully to help decipher the chemical architecture of the human nervous system. The results of these studies are of great importance for the understanding and treatment of neurological and psychiatric disorders such as Alzheimer’s, Parkinson’s and Huntington’s diseases, as well as depression and schizophrenia. Professor Istvan Tork was a pioneer in the chemical anatomy of the brain and carried out important studies on the neuroanatomy and distribution of neuropeptides and monoarnines in the brain; some of his best known work dealt with the dual innervation of the cortex by neurons containing serotonin. Istvan Tork died on November 21, 1992, after a long struggle with a temporal lobe glioma, leaving a profound legacy of friendship and scholarly work 1. It was decided by the editors of this volume to commemorate his work and the mentors hip he gave to his many students by convening a symposium on neurotransmitters in the human brain. The symposium was held at the University of New South Wales on February 5, 1994, and was attended by over one hundred participants, including many of Professor Tork’s colleagues and students. The papers from this symposium are presented in this volume to stand as a tribute to the breadth and quality of his work and to the energy and achievement of his students.