The Palauan sponge Trachyopsis aplysinoides contains a unique sesquiterpene thiocyanate, (lS*,4S*,6S*,7R*)-4-thiocyanat0-9-cadinene (l), three isothiocyanates, 2-isothiocyanatotrachyopsane (2), (2R*,5R*,lOR*)-2-isothiocyanat0-6-axene (3), and (1S*,4S*,5R*,10S*)-lO-isothiocyanatoguaia-6-ene (4), and a formamide, (2R*,5R*,lOR*)-2-formamid0-6-axene (5). The structures of the thiocyanate 1 and isothiocyanate 2 were determined by X-ray analysis, and the remaining structures were elucidated by interpretation of spectral data. The carbon skeleton of isothiocyanate 2 had not previously been reported.