functional proﬁling based on gene modules (e.g. gene ontology or KEGG pathway gene sets) to gene sets based on PPIs. SNOW has been operative since last summer and it has been used by projects associated to the Spanish National Bioinformatics Institute (http:// www.inab.org), the Spanish Network of Cancer (RTICC; http://www.rticcc.org) and the Network of Centres for Research in Rare Diseases (CIBERER, http://www.ciberer.es). SNOW is running in a high-end cluster with 10 dedicated Intel XEON Quad-Core CPUs at 2.0 GHz (summing up a total of 40 cores) with a large amount of RAM (total 60 GB). The program is available at http://snow.bioinfo.cipf.es. SUPPLEMENTARY DATA Supplementary Data are available at NAR Online. FUNDING Spanish Ministry of Science and Innovation (BIO2008-04212 to JD). The CIBER de Enfermedades Raras is an initiative of the ISCIII. The RTICC is an initiative of the ISCIII. The National Institute of Bioinformatics (www.inab.org) is a platform of Genoma Espan˜ a. 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