The AAindex database, a comprehensive resource for amino acid properties, has been updated to include a new section on protein contact potentials. The database now consists of three sections: AAindex1, which contains 544 amino acid indices; AAindex2, which includes 94 amino acid substitution matrices; and AAindex3, which features 47 amino acid contact potential matrices. These data are derived from published literature and are available through the DBGET/LinkDB system at GenomeNet or via anonymous FTP. The addition of contact potentials enhances the database's utility in bioinformatics research, particularly in predicting protein structures and understanding residue-residue interactions. The database is regularly updated and can be accessed through various tools and libraries, such as BioRuby and EMBOSS.The AAindex database, a comprehensive resource for amino acid properties, has been updated to include a new section on protein contact potentials. The database now consists of three sections: AAindex1, which contains 544 amino acid indices; AAindex2, which includes 94 amino acid substitution matrices; and AAindex3, which features 47 amino acid contact potential matrices. These data are derived from published literature and are available through the DBGET/LinkDB system at GenomeNet or via anonymous FTP. The addition of contact potentials enhances the database's utility in bioinformatics research, particularly in predicting protein structures and understanding residue-residue interactions. The database is regularly updated and can be accessed through various tools and libraries, such as BioRuby and EMBOSS.