The structure of halichondramide (2), an antifungal macrolide from the Pacific sponge Halichondria sp., was elucidated by interpretation of spectral data. Two recent reports have provided evidence that the eggmasses of certain nudibranchs are chemically protected against predation. Two macrolides possessing antitumor and antifungal properties were obtained from the eggmasses of Hexabranchus sanguineus and a third bioactive macrolide, kabiramide C (1) was isolated from unassigned eggmasses collected at Kabira Bay, Ishigaki-jima Island.1 We have recently isolated kabiramide B and C from the sponge Halichondria sp. collected in Palau.3 We now wish to report the structural elucidation of halichondramide (2), a related antifungal macrolide from a species of Halichondria from Kwajelein Island.