Methods that aim at predicting interaction partners are very likely to play an important role in the interpretation of genomic information. iSPOT (iSpecificity Prediction Of Target) is a web tool (accessible at http://cbm.bio.uniroma2.it/iSPOT) developed for the prediction of protein-protein interaction mediated by families of peptide recognition modules. iSPOT accesses a database of position specific residue-residue interaction frequencies for members of the SH3 and PDZ protein domain families. The software utilises this database to provide a score for any potential domain peptide interaction.ISPOT: 1. evaluates the likelihood of the interaction between any of the peptides contained in an input protein and a list of domains of the two different families; 2. searches in the SWISS-PROT database for potential partners of a query domain; and 3. has access to a repository of all the domain/target peptide interaction data.