The structures of two new didemnins ([Hysp2]didemnin B and [Hap2]didemnin B) from the Aplousobranch ascidian Trididemnum cycmophorum (Didemnidae) are described. Structures are determined by a combinafon of mass spectrometry and one and two-dimensional high-field NMR techniques. Complete IH and 13C NMR spectral assignments and conformational informations are presented. The cytotoxicities of the compounds towards drugsensitive and drug-resistant tumor cell lines are compared with those of didemnins A and B.