IDEAL, Intrinsically Disordered proteins with Extensive Annotations and Literature (http://www.ideal.force.cs.is.nagoya-u.ac.jp/IDEAL/), is a collection of knowledge on experimentally verified intrinsically disordered proteins. IDEAL contains manual annotations by curators on intrinsically disordered regions, interaction regions to other molecules, post-translational modification sites, references and structural domain assignments. In particular, IDEAL explicitly describes protean segments that can be transformed from a disordered state to an ordered state. Since in most cases they can act as molecular recognition elements upon binding of partner proteins, IDEAL provides a data resource for functional regions of intrinsically disordered proteins. The information in IDEAL is provided on a user-friendly graphical view and in a computer-friendly XML format.