The present volume represents the proceedings of the symposium on npyridine Nucleotide-Dependent Dehydrogenases" which was held on the campus of the re­ cently established University of Konstanz, Germany, from September 15 to 20, 1969. The aim of the symposium was to provide a forum for discussion among the experts interested in the various aspects of pyridine nucleotide-dependent de­ hydrogenases and the pyridine coenzymes, so as to evaluate the state of the present knowledge and to stimulate further progress in this field. In order to facilitate discussion and personal contact it was necessary to restrict the number of participants to 90 including the invited speakers, who came from fifteen countries (Australia, Austria, Denmark, England, Finland, France, Germany, Hungary, Israel, Italy, Japan, Netherlands, Sweden, Switzerland, USA). The printed lectures in this volume differ only in minor respects from those circulated be fore the meeting. In some cases speakers presented new experimen­ tal material during the symposium which was added as an addendum to the papers. The discussions were not recorded. The participants were requested to provide a written report of what they considered worth including in the published re­ port. This, together with the answers of the speakers is presented in this vo­ lume. I whish to thank all the speakers and discussants for their cooperativity in preparing the manuscript. The symposium was sponsored by the International Union of Biochemistry whose President, Professor Theorell, was also present and who was acting as one of the speakers and chairmen.