This Report reviews the literature of marine natural product chemistry for 1997, following earlier reports in this journal covering the period from 1977 to December 1996. The most striking change in 1997 was the sudden increase in reports of new metabolites from marine microorganisms, though the general level of activity in describing new marine natural products declined slightly for the first time. Sponge metabolites continue to dominate new compound reports, but there is growing interest in their potential production by associated microorganisms. Additionally, more marine natural products are being selected for synthesis and in-depth investigations of their biological properties from both biomedical and ecological (e.g., biofouling) viewpoints, and marine natural product chemistry remains a vigorous discipline with room to expand. The review format aligns with its predecessors: it focuses on novel marine natural products with interesting biological and pharmaceutical properties, omitting biochemical studies, biosynthesis research, primary metabolites, detailed pharmacological studies, patent literature, and conference abstracts. In synthetic organic chemistry, the review emphasizes total syntheses that confirm or redefine chemical structures. The majority of 1997 reviews on marine natural products chemistry clustered in topical areas: marine microbiology (e.g., secondary metabolites from marine microorganisms, amphidinolides), marine chemical ecology (e.g., Antarctic marine invertebrates, biofilm regulation, larval settlement/metamorphosis), specific compound classes (e.g., tunichromes, polypropionate-derived 4-pyrones, manzamines, alkylpyridine alkaloids), and other topics (e.g., sea hares, insecticidal agents, Sarcophyton soft corals, starfish toxins, bioactive compounds). A multidisciplinary treatise on sponges (proceedings of a Lake Biwa meeting) with contributions relevant to natural product chemists is also noted.