Four new beta-carboline-based metabolites, didemnolines A-D (1-4), were isolated along with eudistomin O (5), beta-carboline (6), and 2-(2',4'-dibromophenoxy)-3,5-dibromophenol (7) from an ascidian of the genus Didemum, collected near me island of Rota, Northern Mariana Islands. These new beta-carboline-based metabolites differ from most previously isolated compounds in that they are substituted at the N9 position of the beta-carboline ring, rather than the C1 position.