This Report is a review of the literature of marine natural product chemistry for 1993, with a format identical to that of previous reports covering the period from 1977 to December 1992. It does not provide comprehensive coverage of all research involving chemicals from marine organisms but concentrates on reports of novel marine natural products with interesting biological and pharmaceutical properties. Biochemical studies involving marine organisms, reports of primary metabolites, research on the biosynthesis of marine natural products (reviewed in detail elsewhere), papers detailing pharmacological studies, methodology directed toward the synthesis of marine natural products, patent literature, and conference abstracts are omitted. Many excellent reviews of specific areas of marine natural products chemistry appeared during 1993, including a special edition of Chemical Reviews dedicated to the field (covering topics such as chemical studies of marine bacteria, microalgal metabolites, biosynthesis of marine natural products and sterol side chains, bioactive metabolites of symbiotic marine microorganisms, ascidians, bioactive sponge peptides, carbocyclic oxylipins, marine pyridoacridine alkaloids, polyoxygenated steroids, marine toxins, marine invertebrate chemical defenses, Conus peptides, and marine haloperoxidases) and plenary lectures from the 7th International Marine Natural Products Symposium published in two editions of Gazzetta Chimica Italiana.