Recent progress on enzyme immobilisation, enzyme production, coenzyme re­ generation and enzyme engineering has opened up fascinating new fields for the potential application of enzymes in a large range of different areas. As more progress in research and application of enzymes has been made the lack of an up-to-date overview of enzyme molecular properties has become more appar­ ent. Therefore, we started the development of an enzyme data information sys­ tem as part of protein-design activities at GBF. The "Enzyme Hand­ present book book" represents the printed version of this data bank. In future a computer searchable version will be also available. The enzymes in this Handbook are arranged according to the Enzyme Com­ mission list of enzymes. Some 3000 "different" enzymes will be covered. Fre­ quently enzymes with very different properties are included under the same EC number. Although we intend to give a representative overview on the char­ acteristics and variability of each enzyme the Handbook is not a compendium. The reader will have to go to the primary literature for more detailed information. Naturally it is not possible to cover all the numerous literature references for each enzyme (for special enzymes up to 40000) if the data representation is to be concise as is intended.