The UCSC Genome Browser, a comprehensive resource for biomedical research, has been updated with new data and features as of September 2009. The browser now provides genomic sequence and annotation tracks for 47 organisms, including 14 mammals, 10 non-mammalian vertebrates, 3 invertebrate deuterostomes, 13 insects, 6 worms, and a yeast. Key updates include an updated human genome browser, a 44-species multiple sequence alignment track, improved variation and phenotype tracks, and 16 new ENCODE tracks. New features such as drag-and-zoom navigation, a Wiki track for user-added annotations, custom track formats (bigBed and bigWig), a multiple alignment output tool, links to variation and protein structure tools, enhanced in silico PCR utility, and improved track configuration tools have been introduced. The browser also supports bulk downloads of data and offers tools for visualizing and analyzing genome sequences and annotation tracks. Future plans include incorporating more assemblies, improving performance, and enhancing the user interface.The UCSC Genome Browser, a comprehensive resource for biomedical research, has been updated with new data and features as of September 2009. The browser now provides genomic sequence and annotation tracks for 47 organisms, including 14 mammals, 10 non-mammalian vertebrates, 3 invertebrate deuterostomes, 13 insects, 6 worms, and a yeast. Key updates include an updated human genome browser, a 44-species multiple sequence alignment track, improved variation and phenotype tracks, and 16 new ENCODE tracks. New features such as drag-and-zoom navigation, a Wiki track for user-added annotations, custom track formats (bigBed and bigWig), a multiple alignment output tool, links to variation and protein structure tools, enhanced in silico PCR utility, and improved track configuration tools have been introduced. The browser also supports bulk downloads of data and offers tools for visualizing and analyzing genome sequences and annotation tracks. Future plans include incorporating more assemblies, improving performance, and enhancing the user interface.