To identify the genes and gene functions that underlie key aspects of legume biology, researchers have selected the cool season legume Medicago truncatula as a model system for legume research. The mission of the M. truncatula Consortium is to promote unrestricted sharing of data and information that are provided by Medicago research groups worldwide. Through integration of a variety of data and tools, the medicago.org site intends to facilitate progress in the fields of structural, comparative, and functional genomics. To this goal, and as a consortium partner, the Center for Computational Genomics and Bioinformatics (CCGB) at the University of Minnesota has developed MtDB2.0, the M. truncatula database version 2.0. The MtDB2.0 database is the first step toward the global integration of M. truncatula genomic, genetic, and biological information. MtDB2.0 is a relational database that integrates M. truncatula transcriptome data and provides a wide range of user-defined data mining options. The database is interrogated through a series of interfaces, with 58 options grouped into two filters. Sequence identifiers from all public M. truncatula sites [e.g., IDs from GenBank, CCGB, The Institute for Genomic Research (TIGR), National Center for Genome Resources (NCGR), and I'Institut National de la Recherche Agronomique (INRA)] are fully cross-referenced to facilitate comparisons between different sites, and hypertext links to the appropriate database records are provided for all queries' results. MtDB's goal, is to provide researchers with the means to quickly and independently identify sequences that match specific research interests based on user-defined criteria. MtDB2.0 offers unrestricted access to advanced and powerful querying tools unmatched by any other public databases. Structurad Query Language (SQL)-encoded queries with a Java-based Web user interface, incorporate different, filtering that, allow sophisticated data mining of the expressed sequence tag sequencing project results, including the CCGB M. truncatula Unigene set generated with the Phrap assembler. The underlying database and query software have been designed for ease of updates and portability to other model organisms. Public access to the database is at http://www.medicago.org/MtDB.