Barangamide A has been isolated from the sponge Theonella swinhoei, collected at Baranglompo Island, Indonesia, and the structure elucidated by interpretation of special data and application of Marfey's method. Barangamide A is a cyclic undecapeptide possessing three N-methylated amino acids, three fl-alanine and the same amino acid sequence with the ring portion of the known theonellapeptolide IId isolated also in the present work. The theonellapeptolides have been reported to have moderate cytotoxicity, whereas barangamide A was inactive at the same concentration. © 1999 Elsevier Science Ltd. All rights reserved