Amplicon is a program for designing PCR primers on aligned groups of DNA sequences. The most important application for Amplicon is the design of 'group-specific' PCR primer sets that amplify a DNA region from a given taxonomic group but do not amplify orthologous regions from other taxonomic groups. AVAILABILITY: Amplicon is freely available as a script that will run on any platform with Python 2.3 installed (http://www.python.org). It is also available as a Windows executable. Free downloads that do not require registration can be found at http://www.aad.gov.au/amplicon