teps. First, we abstracted protein interactions onto orthologous cluster links. For a given source interaction, if both proteins belonged to a cluster, we constructed a link between these two clusters. In the second step, we projected these cluster links onto a specific target species. Practically, for a given link, if both clusters contained a protein from the target species, we predicted an interaction between these proteins. Results We applied our automated prediction tool to the cyanobacteria Synechocystis. It enabled us to predict a new network of 1,463 protein-protein interactions when less than 200 interactions were experimentally annotated in the databases. In the same way, we predicted for instance 13,469 interactions for the rat. Availability This open-source application can either be run online through a web interface or downloaded at http:// biodev.extra.cea.fr/interoporc/. To run the tool online, we have collected source interactions from the three manually curated databas...