Repbase Update is a comprehensive database of repetitive elements from diverse eukaryotic organisms. Currently, it contains over 3600 annotated sequences representing different families and subfamilies of repeats, many of which are unreported anywhere else. Each sequence is accompanied by a short description and references to the original contributors. Repbase Update includes Repbase Reports, an electronic journal publishing newly discovered transposable elements, and the Transposon Pub, a web-based browser of selected chromosomal maps of transposable elements. Sequences from Repbase Update are used to screen and annotate repetitive elements using programs such as Censor and RepeatMasker. Repbase Update is available on the worldwide web at http://www.girinst.org/Repbase_Update.html.