The isolation and structure determination of an unusual cyclic heptapeptide, wainunuamide, from a Fijian marine sponge, Stylotella aurantium, is reported. The peptide contains three proline residues and a histidine residue, which is rare in cyclic peptides and has only previously been reported in a cyclic peptide isolated from the cyanobacterium Oscillatoria agardhii, suggesting a possible source of the peptide. Wainunuamide is found to have weak cytotoxic activity.