The defensins knowledgebase is a manually curated database and information source focused on the defensin family of antimicrobial peptides. The current version of the database holds a comprehensive collection of over 350 defensin records each containing sequence, structure and activity information. A web-based interface provides access to the information and allows for text-based searching on the data fields. In addition, the website presents information on patents, grants, research laboratories and scientists, clinical studies and commercial entities pertaining to defensins. With the rapidly increasing interest in defensins, we hope that the knowledgebase will prove to be a valuable resource in the field of antimicrobial peptide research. The defensins knowledgebase is available at http://defensins.bii.a-star.edu.sg/.