Biomolecule phosphorylation by protein kinases is a fundamental cell-signaling process in all living cells. Following the comprehensive cataloguing of the kinase complement of the human genome by Manning, this paper will detail the state-of-the-art human and mouse kinase proteomes as provided in the UniProtKB/Swiss-Prot protein knowledgebase. The sequences of the 480 classical and up to 24 atypical protein kinases now believed to exist in the human genome and 485 classical and up to 24 atypical kinases within the mouse genome have been reviewed, and where necessary, revised. Extensive annotation has been added to each entry. In an era when a wealth of new databases is emerging on the internet, UniProtKB/Swiss-Prot makes available to the scientific community the most up-to-date and in-depth annotation of these proteins, with access to additional external resources linked from within each entry. Incorrect sequence annotations resulting from errors and artefacts have been eliminated. Each entry will be constantly reviewed and updated as new information becomes available, with the orthologous enzymes in related species being annotated in a parallel effort and complete kinomes being completed as sequences become available. This ensures that the mammalian kinomes available from UniProtKB/Swiss-Prot are of a consistently high standard, with each separate entry acting both as a valuable information resource and a central portal to a wealth of further detail via extensive cross-referencing.