A novel cyclic peptide, oriamide (1) containing the new 4-propenoyl-2-tyrosylthiazole amino acid (PTT), was isolated from the marine sponge Theonella sp. collected in Sodwana Bay. The structure of oriamide, including the absolute configuration of all amino acids, was elucidated by spectroscopic analysis and degradation experiments. © 1997 Elsevier Science Ltd.