Abstract Summary: We have developed a set of tools to construct positional weight matrices from known transcription factor binding sites in a species or taxon-specific manner, and to search for matches in DNA sequences. Availability: PROMO can be accessed online at http://www.lsi.upc.es/~alggen under the research link. Supplementary information: An example of the graphic interface (Figure 1) can be visualized at http://www.lsi.upc.es/~alggen/recerca/promo/figuraBioinformatics.html. Contact: [email protected]; [email protected] * To whom correspondence should be addressed.