Springer Handbook of Enzymes provides data on enzymes sufficiently well characterized. It offers concise and complete descriptions of some 5,000 enzymes and their application areas. Data sheets are arranged in their EC-Number sequence and the volumes themselves are arranged according to enzyme classes. There exist about 57,000 synonyms for the 5,000 enzymes. The Synonym Index helps in finding the recommended name for a given enzyme. It is also correlated with the EC number and the volume and page number of the corresponding place in the Springer Handbook of Enzymes. Since the publication of the first Synonym Index in 2001, the number of synonyms have more than doubled (from 25,000 to 57,000). Thus, the Synonym Index 2010 lists all current synonyms and supplements the correlated volume and page number for all volumes.