Since the last compilation of restriction enzymes (1), 300 new entries have been added including 12 new specificities. With the growing size of this database and the recognition that the most widespread use of the information is as a database for computer programs predicting restriction enzyme cleavage patterns, the new format has been continued. This format is intended to contain the minimal amount of information required by a computer program. It should be noted that only enzymes for which the recognition sequence is known are included. This new list is shown"in the first Table, while an alphabetical listing of all Type II enzymes is presented in the second Table. A copy of the restriction enzyme data base in its previous format (2), including enzymes of unknown recognition sequence, will be available upon request. It should also be noted that an alternative compilation of these enzymes has recently been produced (3).