This Report is a review of the literature of marine natural product chemistry for 1994. Earlier reports published in this journal cover the period from 1977 to December 1993. The format for this review is identical to that of the previous reports, except that compounds from cyanobacteria (or blue-green algae) are now included in the section on marine microorganisms and phytoplankton. The review does not provide a 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 and reports of primary metabolites are specifically omitted. Research on the biosynthesis of marine natural products has been reviewed in detail elsewhere and is not included in this report. Wherever possible, the biological and pharmacological properties of new marine natural products have been reported but papers detailing the pharmacological studies are beyond the scope of this review. In the area of synthetic organic chemistry, the review focuses on reports of the total synthesis of marine natural products or close analogues, particularly those papers that redefine chemical structures. No attempt has been made to review the patent literature or conference abstracts and reports.