The second U.S.-Japan Seminar on "Bioorganic Marine Chemistry" was held in Honolulu, Hawaii, 3-7 December, 1990. Twenty-one invited lecturers and fourteen observers from the two countries attended. Recent results in the areas of (a) new bioactive natural products, (b) biological and pharmacological activity of marine natural products, and (c) biosynthesis of marine natural products were presented and discussed. Summaries of the presentations and relevant chemical structures are presented in this report.