From both ecological and biomedical viewpoints, it has become importan
t to know whether the metabolites isolated from sponges are produced b
y symbiotic micro-organisms. Certain halogenated metabolites from Dysi
dea herbacea are localized in the symbiotic cyanobacterium Oscillatori
a spongeliae. Recent studies concerning the origin of bioactive metabo
lites from lithistid sponges, some of which contain filamentous micro-
organisms, are presented.