Novel dibromotyrosine-derived metabolites, ianthesines A, B, C, and D, were isolated from an Australian marine sponge of the genus Ianthella sp. Their structures were elucidated using chemical and spectroscopic techniques. Ianthesines A, B, and D were derived from two dibromotyrosines. Ianthesine C is a tetramer possessing eight bromine atoms and its molecular weight is 1606. Ianthesines B–D showed