The present invention relates to combinations of 4-bromo-2-(4-chloro-phenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile- , or a salt thereof, and copper or zinc compounds which provide an improved protecting effect against fouling organisms. More particularly, the present invention relates to compositions comprising a combination of 4-bromo-2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile, or a salt thereof, together with one or more copper or zinc compounds selected from Cu.sub.2O, Cu(OH).sub.2, CuSO.sub.4, copper pyrithione, CuSCN, CuCO.sub.3, ZnO, ZnCl.sub.2, ZnSO.sub.4, zineb, and zinc pyrithione; in respective proportions to provide a synergistic effect against fouling organisms and the use of these compositions for protecting materials against fouling organisms. This invention thus relates to the field of protection of materials, such as underwater objects, protection of wood, wood products, biodegradable materials and coatings.