The present invention relates to combinations of pyrimethanil, or a salt thereof, and a monoterpene, or a salt thereof, which provide an improved biocidal effect. More particularly, the present invention relates to compositions comprising a combination of pyrimethanil, or a salt thereof, together with a monoterpene selected from thymol and β-thujaplicin in respective proportions to provide a synergistic biocidal effect. Compositions comprising these combinations are useful for the protection of any living or non-living material, such as crops, plants, fruits, seeds, objects made of wood, thatch or the like, engineering material, biodegradable material and textiles against deterioration due to the action of microorganisms such as bacteria, fungi, yeasts, algae, viruses, and the like.