Marine biotoxicology is the science that deals with the poisons produced by marine plants and animals. This subject is briefly reviewed in an attempt to provide an overview of the subject as it pertains to analytical toxicology, and to provide a brief résumé of the chemical structure, toxicity, and mechanism of action of these poisons. Subjects discussed include marine phytotoxicology, protozoan, sponge, coelenterate, echinoderm, mollusk, nemertine, annelid worm, crab, stingray, weeverfish, scorpionfish, ciguatoxin, tetrodotoxin, scombrotoxin, sea snake, turtle, and mammal poisons. Knowledge of the therapeutics of marine biotoxications is still quite meager. Knowledge of the nature and mechanism of action of these biotoxins is essential to a more scientific approach to the treatment of their intoxications.