Abstract: The inventors provide a composition comprising an antimicrobial polypeptide comprising Blad or an active variant thereof for use in a method of treatment of the human or animal body by therapy or prophylaxis, such as for use in a method of treating or preventing an infection in or on a subject by a microorganism. Also provided is the use of a composition comprising an antimicrobial polypeptide comprising Blad or an active variant thereof to kill, or inhibit the growth of, a microorganism that is pathogenic to a human or an animal at a site that is not on or in the human or animal body.