PARSESNP is a tool for the display and analysis of polymorphisms in genes. Using a reference DNA sequence, an exon/intron position model and a list of polymorphisms, it determines the effects of these polymorphisms on the expressed gene product, as well as the changes in restriction enzyme recognition sites. It shows the locations and effects of the polymorphisms in summary on a stylized graphic and in detail on a display of the protein sequence aligned with the DNA sequence. The addition of a homology model, in the form of an alignment of related protein sequences, allows for prediction of the severity of missense changes. PARSESNP is available on the World Wide Web at http://www.proweb.org/parsesnp/.