The GCG programs, also called the “Wisconsin Package,” comprise a powerful suite of tools for manipulating, analyzing, and comparing nucleotide and protein sequences (1 ). The initials GCG stand for Genetics Computer Group, which is a subsidiary of Oxford Molecular Group (Campbell, CA). The Wisconsin Package includes more than 130 programs, each of which functions as a tool for performing a specific task, such as translating a nucleotide coding sequence or determining restriction enzyme cutting sites. Most GCG programs use one file as input and write the results to another file. The output files from many GCG programs are suitable as input to other GCG (or other) programs. In many cases, complex problems can be solved by using several GCG programs in succession.