ACT (Artemis Comparison Tool) is a DNA sequence comparison viewer based on Artemis. In common with Artemis, ACT is written in Java and runs on UNIX, GNU/Linux, Macintosh and MS Windows systems. It can read complete EMBL and GENBANK entries or sequence in FASTA or raw format. Extra sequence features can be in EMBL, GENBANK or GFF format. ACT is distributed under the same license as Artemis. The sequence comparison displayed by ACT is usually the result of a blastn or tblastx search that has been processed by MSPcrunch. MSPcrunch must be run with the -d flag for the output to be usable by ACT.