Proteinortho is a tool to detect orthologous genes within different species. For doing so, it compares similarities of given gene sequences and clusters them to find significant groups. The algorithm was designed to handle large-scale data and can be applied to hundreds of species at one. Details can be found in Lechner et al., BMC Bioinformatics. 2011 Apr 28;12:124 (http://www.biomedcentral.com/1471-2105/12/124). To enhance the prediction accuracy, the relative order of genes (synteny) can be used as additional feature for the discrimination of orthologs. The corresponding extension, namely PoFF (manuscript in preparation), is already build in Proteinortho.