The present invention relates to compositions comprising a combination of pyrimethanil, or a salt thereof, together with one or more silver salts selected from silver acetate, silver alginate, silver azide, silver citrate, silver lactate, silver nitrate, silver sulfate, silver chloride, silver thiocyanate, silver-sodium-hydrogen-zirconium phosphate, silver sulfadiazine, silver cyclohexanediacetic acid and disilver 2,5-dichloro-3,6-dihydroxy-2,5-cyclohexadiene-1,4-dione; in respective proportions to provide a synergistic biocidal effect. Another suitable silver component (II) is nano-silver particles, typically with a particle size of 1-1000 nm. Compositions comprising these combinations are useful for the protection of any living or non-living material against deterioration due to the action of microorganisms such as bacteria, fungi, yeasts, algae, and the like.