Direct sequencing of PCR products using the dideoxy chain termination procedure developed by Sanger et al. (1) is now the most commonly used method for defining specific mutations. The main benefits of this method lie in its ease of use and this has been enhanced in recent years by the introduction of fluorescent labels and automated detection systems which obviate the need for radioactivity. Although the initial purchase price for automated sequencers is high, this is compensated for by single-tube reaction chemistry and rapid analysis and base calling.