Compositions of matter which include 1, 2-benzisothiazolin-3-one (also known as "BIT") and a divalent metal carboxylate and exhibit desirable activity for inhibiting microbial growth are described. Methods for preserving an aqueous solution or dispersion from degradation by bacteria or fungus, and methods for preserving a dry film from degradation by bacteria or fungus, are also described. The inventive mixtures provide greater antimicrobial protection per unit mass of metal carboxylate and BIT against certain microbes than is exhibited per unit mass by the metal carboxylate alone or by BIT alone. Desirable antimicrobial activity has been observed with mixtures of the invention against Pseudomonas aeruginosa, Escherichia coli, Enterobacter aerogenes, and Alcaligenes faecalis, among others.
