Malevamide D (1), a highly cytotoxic peptide ester, and the known compound curacin D (5) were isolated from a Hawaiian sample of Symploca hydnoides. The structure of 1 was elucidated by spectroscopic analysis including NMR and high-resolution MS/MS. Partial stereochemical assignments of 1 were made by chiral HPLC analysis of acid and base hydrolysates. Malevamide D (1) demonstrated toxicity against P-388, A-549, HT-29, and MEL-28 cell lines in the subnanomolar range, while curacin D (5) was weakly cytotoxic. Malevamide D (1) is closely related to isodolastatin H (2), which was previously isolated in low yield from the sea hare Dolabella auricularia. A second Hawaiian sample of S. hydnoides yielded curacin D (5) along with the known dolastatin-10 analogue symplostatin-1 (3).