The objective of the Enzyme Handbook is to provide in a concise form data on enzymes sufficiently well characterized. Data of about 3000 enzymes are presently known and their data sheets will be published at a frequency of 200 per quarter. The data sheets are arranged in their EC Number sequence, starting with Classes 4 and 5/6 (Lyases and Isomerases/Ligases, respectively) in Volumes 1 and 2. For each enzyme, systematic and common names are given, information on reaction type, substrate and product spectrum, inhibitors, cofactors, kinetic data, pH and temperature range, origin, purification, molecular data and storage conditions are listed. A reference list completes the data sheet. This collection is an indis- pensable source of information for researchers applying enzymes in analysis, synthesis and biotechnology.