Applicants have discovered that cyclic and acyclic ketone acids, such as dehydroacetic acid, and salts thereof as well as an aromatic carboxylic acid and salts thereof enhance the performance of iodine containing biocides as antimicrobial agents and preservatives. The present invention provides a composition comprising (a) an iodine containing biocide; and (b) (i) a ketone acid or salt thereof, (ii) an aromatic carboxylic acid or a salt thereof, or (iii) a mixture thereof. Preferably, the ketone acid is a cyclic ketone acid and the aromatic carboxylic acid is salicylic acid.