This Report is a review of the literature of marine natural product chemistry for the period 1 December 1987 to the end of 1988. It is the sixth in a series of reviews published in Natural Product Reports, with the earlier ones covering the period from 1977 to December 1987. Like the earlier reports in this series, this review does not comprehensively cover all research involving chemicals from marine organisms but focuses on papers reporting novel marine natural products with interesting biological and pharmaceutical properties. Biochemical studies involving marine organisms and reports of primary metabolites are specifically omitted. Research on the biosynthesis of marine natural products has been reviewed in an excellent report by Garson. Due to the expanded interest in the pharmacological properties of marine natural products, tracking the literature in this area has become much more difficult. While every effort has been made to record the pharmacological activity of new metabolites, studies on mechanisms of action and reports of basic pharmacology using marine natural products as biological probes are reviewed only when they result in a significant change in the biomedical status of a compound. In the field of synthetic organic chemistry, reports on the total synthesis of marine natural products or their close analogues are included, but papers dealing with methodology directed at the synthesis of marine natural products are omitted. No attempt has been made to review patent literature or conference abstracts and reports. During the reporting period, two volumes of a new series of interpretive reviews appeared, covering topics such as 'Natural Product Chemistry and Chemical Defense in Tropical Marine Algae of the Phylum Chlorophyta', 'Chemical Ecology of the Nudibranchs', 'Marine Metabolites which Inhibit Development of Echinoderm Embryos', 'The Search for Antiviral and Anticancer Compounds from Marine Organisms', 'Chemistry of Aqueous Marine Extracts: Isolation Techniques', 'Secondary Metabolites from Echinoderms as Taxonomic Markers', 'The Chemical Ecology of Alcyonarian Corals', and 'Chemical Defense in Fishes'.