The picture on the following page is being reproduced here, at the request of the partici pants in the Advanced Research Workshop "Amino Acid Availability and Brain Function in Health and Disease." I displayed this limewood carving, entitled "Neurochemistry," during my closing remarks to this extraordinarily stimulating and productive workshop so ably organized by my collaborator Dr. Gerald Huether. We scientists need two sturdy legs to carry us through all the twists and turns of our academic careers. We should also have, as it were, a reserve leg handy, to help us stay upright when this career ends. My "third leg" is wood carving. The idea for "Neurochemis try" came to me in the plane carrying me to the congress of the International Neuro chemical Society in Jerusalem. We need the hands for our meticulous experimental work, and at least one ear to listen to the messages our neurons send us. A few years ago it would have been premature to hold a workshop on this subject. Now, however, the time was just right to allow an overview of the status of current re search, and to point out the promising new openings it has created. There is no doubt that the book to be published as a result of this workshop will be, for the next years at least, the standard text on the subject. Hearty thanks to all speakers for their brilliant con tributions and to all participants for the lively, uninhibited and stimulating discussion."

This volume contains the proceedings of the Ninth Meeting of the "International Study Group for Tryptophan Research" (lSTRY), held at the University of Hamburg, Germany, from October 10 to 14, 1998. At this meeting the recent developments in the field of tryptophan research were presented by leading researchers from all over the world in 81 oral and 48 poster contri butions. Research on tryptophan and its derivatives provides an inexhaustible subject. At the conference we tried to compose a multifacetted picture of the recent investiga tions through contributions from the major disciplines involved. Thus, we tried to strike a balance between basic research topics and clinical, nutritional or industrial applica tions. We offered workshops on tryptophan (in sleep and mood), melatonjn, IDO-acti vation and the eosinophilia-myalgia syndrome (EMS) as a platform for intensive discussion for the participants. In these proceedings many contributions are multidisciplinary and have practical or theoretical implications for different research fields. Hence, we have organized this volume in nine main chapters according to basic disciplines and subjects. We are aware that this classification is artificial, but we hope that it is the best compromise for contributors and readers."