In the five years since the appearance of the Enzyme Handbook several hundred new enzymes have been described. The Supplement includes molecu- lar and kinetic data on about half of these and also on several enzymes omitted from the Handbook, - information on many of the remainder will be found in Enzyme Nomenclature (1972). An incomplete search of the literature may have resulted in the omission of a number of enzymes from the Sup- pleinent and I apologize to the authors whose contributlOns I have misseQ. The labour involved in compiling the data for the Supplement was greatly reduced by the kindness of Professor E. C. Webb who sent me a draft copy of Enzyme Nomenclature (1972) prior to publication. Dr. E. A. Jones ana Dr. G. S. Knaggs reviewed the entire text of the Supplement and I am grateful for their criticisms and suggestions. I also thank-the manYleople who offered constructive criticisms of the earlier Enzyme Handboo . Several of these suggestions have been incorporated into the Supplement. I am grateful to Mrs. Anna Knaggs for her expert typing and for making the manuscript ready for photomechanical reproouction, to Mrs. Lucia Barman for preparing the lists of references and the index and to the staff of Springer-Verlag for giving me every possible assistance in seeing the Supplement to completion. I am indebted to Professor E. C.