A wealth of gene information is accruing in public databases. Genome browsers such as Ensembl are needed to organize and depict this information in the context of the genome. Ensembl provides an open source gene set based on experimental evidence for over 30 species, the majority of which are vertebrates. Genes and annotation are accessible through the Ensembl browser (http://www.ensembl.org), and through direct queries of its databases using the Perl API (Application Programme Interface), MySQL or BioMart.