Clathramide A (1a) and B (1b) are two novel isomeric bromopyrrole alkaloids containing the uncommon N-methylimidazolinium moiety, isolated from the Caribbean sponge Agelas clathrodes. Their structures, elucidated on the basis of a detailed spectroscopic analysis, appear not biosynthetically related to oroidin and its derivatives. In addition, 1a-1b exhibited a mild antifungal activity tested in an agar disk assay on Aspergillus niger. Copyright (C) 1996 Elsevier Science Ltd