Over the past decade, chemical investigations of benthic marine algae have illustrated that these organisms producea wide variety of structurally unique and biologically active secondary metabolites. Reviews of many aspects of these studies can be found in the various volumes of the treatise entitled ‘Marine Natural Products’ edited by Scheuer (1978–81). In general, it has been discovered that many of the red algae (Rhodophyta) produce halogenated terpenoids and acetogenins (compounds produced by acetate polymerization), and that the main halogen involved in this synthesis is bromine (Fenical 1975, 1982). Many of the halogenated metabolites have shown antimicrobial activities, cytotoxicities, and other pharmacological effects, and by virtue of their halogen substituents, these compounds have also been considered as leads for the development of new agrichemicals.