The author has reviewed the classification, the nomenclature and the ecological aspects of biologically active compounds, emphasizing the Freyvogel & Perret's (1973) concepts of venomous and poisonous organisms. The literature involving the phyla Annelida, Mollusca and Arthropoda was also reviewed. The author's pharmacological studies performed with the polychaete Eurytlioe camplanata, which revealed a dializable principle, active in the guinea pig's ileum and dorsal muscle ot polvchaete itself are also commented. This principle differs from Acetylcholine and Serotonin. Pharmacologically studies in the sea-hares (genus Aplysia) were also focused, including the author's contribution. In the glands os Aplysia brasiliana, namely the mid-gut-gland, the opaline gland and the purple gland, the author confirmed presence of cholinesters, which are discussed in the review. Toxicity of Arthropods are also discussed, mainly in decapod crustaceans. In some Brazilian crabs studies revealed a pharmacological activity of the gastric secretion expelled with an apparently defensive purpose and its ecological importance is focused in terms of the community. The relatively scarce studies of chemical ecology of marine organisms in Latin America and the importance of these studies were finally emphasized.