Here we describe the development of a genome-wide and nonredundant mouse transcription factor database and its viewer (http://genome.gsc.riken.gp/TFdb/). We systematically selected transcription factors with DNA-binding properties and their regulators on the basis of their LocusLink and Gene Ontology annotations. We also incorporated into our database information regarding the corresponding available cDNA clones and their structural properties. Because of these features, our database is unique and may provide useful information for systematic genome-wide studies of transcriptional regulation.