Custom annotation tracks, a popular Genome Browser feature for several years, allow users to load, display and manipulate personal data in the Genome Browser and Table Browser. The new custom tracks manager (http://genome.ucsc.edu/cgi-bin/hgCustom) makes the use of custom tracks much easier. The management interface can be accessed through the ‘add/manage custom tracks’ button on the Genome Browser gateway (http://genome.ucsc.edu/cgi-bin/hgGateway) or tracks (http://genome.ucsc.edu/cgi-bin/hgTracks) page. In addition to the data upload options supported in previous versions, users can now load and display multiple custom tracks simultaneously, add to, delete and modify the uploaded custom track set, load and manage tracks from multiple assemblies, and upload description pages for custom tracks. The lifespan of a custom track on the UCSC server has been increased from 8 to 48 h after last access, and we have converted the underlying custom track architecture from a file-based system to a database system to improve the performance.
