The positions of the modified nucleotides in the rRNA of several well-studied organisms can be visualized in linear, secondary structure and 3D structure formats. The menu bar (top) shows the sections of the database, and portions of the associated links are illustrated in exploded views. The examples shown are for modifications concentrated around the A site and PTC regions of E. coli and human (middle left; upper, view of the A site and PTC, lower, view of the PTC toward the exit tunnel). The 3D arrangements of the modified nucleotides in E. coli and human rRNAs are displayed using bioinformatics tools (middle right) available in a section named ‘Mod sites in 3D’. An interactive interface is provided for controlling the views of the ribosome model (both subunits, and the A-, P- and E-site tRNAs, and mRNA) and for selecting modifications, as follows: ‘pseudouridines’ (red), ‘2′-O-methylations’ (green) and ‘base methylations’ (orange). The web service is heavily linked to material in other databases and web resources, for example, snoRNA databases for human, yeast and plants, Modomics (a database of RNA modification pathways), EcoCyc (a comprehensive genome database for E. coli) and PubMed.