This volume is a compilation of the presentations and discus sions, arranged in a systematic manner, of the fifth symposium on the Search for the Causes of Schizophrenia, held in Guarujal Brazil in April, 2003. The meetings look back on a great tradi tion. The first symposium, held in 1986 on the occasion of the th 600 anniversary of the University of Heidelberg, was our first effort to assemble successful schizophrenia researchers to pre sent and discuss research results in a spirit overcoming meth odological boundaries and disciplines. The result was one of the most interesting and exciting meetings and a proceedings volume published in 1987. Like the present volume it contained the presentations and discussions of the meeting conveying an excellent picture of what was going on in schizophrenia re search at that time and outlining the main future perspectives. Four further symposia followed at an interval of 2 to 3 years each. They were guided by the same principle and characterised by illustrious contributors and a highly stimulating atmosphere. The proceedings volumes, all entitled "Search for the causes of schizophrenia" and looking alike, were published by the same publisher. They reflect the considerable progress made in schi zophrenia research since 1986 and have been widely used as a source for information on the most promising research lines and results and as a reference for comprehensive reviews.