Anchinopeptolide A (1), a dimeric peptide alkaloid of a completely new type, has been isolated from the marine sponge Anchinoe tenacior collected in the Mediterranean sea along the coasts of Tunisia. The structure elucidation of 1, which include in each half a C-terminal trans 4-hydroxystirylamino residue linked to L-alanine, which in turn is attached to an arginine derived 5-guanidino-2-hydroxy-pentanoyl residue, is described.