REBASE is a comprehensive database of information about restriction enzymes and their associated methylases, including their recognition and cleavage sites and their commercial availability. Also included is a listing of homing endonucleases. Information from REBASE is distributed via monthly electronic mailings as well as through anonymous ftp and the World Wide Web. The REBASE web site (http://www.neb.com/rebase) contains a web page for every enzyme, reference and supplier. Additionally, there is a search facility, help and NEWS pages, and a complete description of our various services. Specialized files are available that can be used directly by many software packages.