Disclosed is a composition comprising a combination of 4-bromo-2-(4-chlorophenyl)-5- (trifluoromethyl)-1H-pyrrole-3-carbonitrile, or a salt thereof, as component (I), and ZnSO4 as component (II)； whereby component (I) and one of the components (II) are in respective proportions to provide a synergistic effect against fouling organisms, wherein the ratio by weight of component (I) to one of the components (II) is 10:1 to 1:10. Also disclosed is a product containing (a) a composition comprising 4-bromo-2-(4-chloro-phenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile, or a salt thereof, as component (I), and (b) a composition comprising ZnSO4 as a component (II), wherein the compounds are administered simultaneously or sequentially, and wherein said (a) and (b) are in respective proportions which in use provide a synergistic effect against fouling organisms, wherein the ratio by weight of component (I) to one of the components (II) is 10:1 to 1:10.
