The UniProt Knowledgebase (UniProtKB) produced by the UniProt Consortium members, is a central repository collecting functional and sequence information on proteins, with accurate, consistent and rich annotation. The current rate at which sequence data is added to UniProtKB far exceeds the rate at which this data can be manually annotated. UniProt has therefore developed automatic annotation systems to enhance protein records in UniProtKB lacking full manual annotation by enriching them with automatic classification and annotation. Central to the automatic annotation systems are rules based on family and domain classification and on published experimental data incorporated in fully manually annotated entries in UniProtKB. In addition, UniProtKB also currently provides over 2,900 complete proteome sets where each set represents the entries that define the proteome of a specific organism, and which are spread over the entire taxonomic range including but not limited to chicken, cow, dog, horse, human, mouse, pig, rat and sheep. In this presentation the automatic annotation procedure in UniProtKB using UniRules and the representation of complete proteomes in UniProtKB will be described. UniProtKB is available at www.uniprot.org. The UniProt Consortium: EMBL-European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SD, UK; Protein Information Resource, Georgetown University Medical Center, 3300 Whitehaven Street, NW, Suite 1200, Washington, DC 20007, USA; Swiss Institute of Bioinformatics, CMU, 1 rue Michel-Servet, 1211 Geneva 4, Switzerland.