The program NIP contains a routine for finding and displaying the positions of the cut sites of restriction enzyme recognition sequences. Linear or circular sequences can be searched, and the results can be listed in various forms or displayed graphically. The recognition sequences to be searched for can be typed on the keyboard or read from files. The format of these files is given in Note 1. The end of the chapter also describes how to produce back-translations of protein sequences so that these routines can be used to search them for restriction sites.