- The sea offers a wide variety of potentially useful resources. Marine algae have been a rich source of structurally unique natural products showing diverse biological properties. The current need to develop new antifungal, antibiotic, anticancer and antiviral drugs has prompted intense research efforts into the discovery, isolation and structure determination of these potential medicinal agents from seaweeds. Over the past two years a survey of the biomedicinal potential of seaweeds from the Oregon Coast has been conducted. In this period we have made 125 survey collections representing some 85 different species of algae. On the basis of antimicrobial bioassays and preliminary chemical characterization, 16 seaweeds have been identified for further study. This research has investigated, using standard chromatographic and spectrochemical techniques including 2D NMR spectroscopy, the natural products of the previously unstudied red alga Ptilota filicina J. Agardh (order: Ceramiales). P. filicina. which grows abundantly on rocks in the midintertidal zones along the central Oregon coast, yielded a unique series of ω-3 fatty acids. Two of them were found to be stereoisomeric icosapentaenoic acids containing conjugated triene functionalities, while a third, ptilodene, was characterized as another novel 20-carbon fatty acid with oxidation sites at C-11 and C-16. Ptilodene showed slight antimicrobial activity to pathogenic gram-negative and gram-positive bacteria, and moderate inhibition to the dog kidney Na⁺/K⁺ ATPase. From a previous survey of marine algae from the Caribbean, the red seaweed Laurencia obtusa (Hudson) Lamouroux (order: Ceramiales) was identified for further investigation. L. obtusa is a recognized source of many novel natural products and occurs worldwide in tropical and subtropical marine habitats. Of the several collections made, the Isleta Marina collection (northeastern coast of Puerto Rico) was shown to possess two novel isomeric brominated sesquiterpenes, in addition to the previously known sesquiterpenes, elatol and obtusol. A minor component of this research was devoted to the isolation of hormothamnione, the first naturally occuring styrylchromone, from the tropical marine cyanophyte Hormothamnion enteromorphoides Grunow. Hormothamnione was found to be a potent cytotoxin to cancer cells in vitro and appears to be a selective inhibitor of RNA synthesis. The results obtained from our survey of Oregon seaweeds contradicts the generally accepted hypothesis that temperate-cold water algae, as versus tropical algae, are devoid of interesting secondary metabolites. The occurrence of novel ω-3 icosapentaenoic acids is of current interest because of their structural similarity to 5Z, 8Z, 11Z, 14Z, 17Z- icosapentaenoic acid, arachidonic acid and related derivatives of these, many of which possess significant hormonal and bioregulatory functions in mammalian systems.