The past decade has been a period of explosion of knowledge on the chemistry and pharmacology of snake toxins. Thanks to the development of protein chemistry, nearly a hundred snake toxins have been purified and sequenced, representing one of the largest families of sequenced proteins. Moreover, the mode of action of these toxins has been largely elucidated by the concerted efforts of pharmacologists, electro physiologists, and biochemists. As a result of these studies, some of the snake toxins, e.g., a-bungarotoxin and cobra neurotoxins, have been extensively used as specific markers in the study of the acetylcholine receptors. Indeed, without the discovery of these snake toxins, our knowledge of the structure and function of nicotinic acetylcholine receptors would not have advanced so rapidly. The contribution of snake venom research to the biomedical sciences is not limited to the study of cholinergic receptors. Being one of the most concentrated enzyme sources in nature, snake venoms are also valuable tools in biochemical research. Venom phosphodiesterase, for example, has been widely used for structural studies of nucleic acids; proteinase, for the sequence studies of proteins and pep tides ; phospholipase A , for lipid research; and L-amino acid oxidase for identifying optical z isomers of amino acids. Furthermore, snake venoms have proven to be useful agents for clarifying some basic concepts on blood coagulation and some venom enzymes, e.g., thrombin-like enzymes and pro coagulants have been used as therapeutic agents.