The present invention relates to combinations of the pyrion compounds sodium pyrithione and 1-hydroxy-2-pyridinone, and polyethyleneimines (PEI) which provide an improved biocidal effect. More particularly, the present invention relates to compositions comprising a combination of a pyrion compound selected from sodium pyrithione and 1-hydroxy-2-pyridinone together with polyethyleneimines； 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.
