New World elapids are coral snakes that belong to the genus Micrurus, and for which the venom biochemistry is mostly unknown. Analysis has been difficult because the coral snakes produce small quantities of venom. Clinical observations following bites show mainly neurotoxic effects. Experimentally, cardiotoxic, haemolytic and myotoxic activities are also reported. An experimental approach, using reverse-phase high-performance liquid chromatography and specific assays for a-neurotoxin and phospholipase A, activities, was conducted on milligram quantities of venoms from three Micrurus species from Costa Rica; M. nigrocinctus nigrocinctus, M. alleni yatesi and M. multifasciatus. Neurotoxicity was determined by competition binding experiments with the Torpedo marmorata acetylcholine receptor. Phospholipase A, activity was measured by fluorimetry using a pyrene lipid substrate. In this way, we purified and characterized seven a-neurotoxins, five phospholipases A, and four toxin homologs. The amino acid sequence of the major a-neurotoxin from M. nigrocinctus nigrocinctus venom was fully determined and compared to Old Word representatives. Distance matrix data were generated to set up phylogeny relationships among elapid short-chain a-neurotoxins, which proved to be in accordance with the taxonomic classification and geographical distribution of snake species.Keywords: Micrurus; a-neurotoxin; phospholipase A, ; venom.The elapid representatives of the New World are coral snakes. They comprise a group of about 120 species and subspecies (genera Micrurus, Leptomicrurus and Micruroides) distributed from Southern United States to Argentina (Mc Dowell, 1987 ;Campbell and Lamar, 1989). Clinical observations following bites show mainly neurotoxic effects, and in severe cases of envenomation, death due to respiratory arrest (Weis and Mc Isaac, 1971;Ramsey et al., 1972;Vital Brazil et al., 1976Moussatche and Melendez, 1979). Experimental studies suggest an extended spectrum of activities in Micrurus venoms. Neurophysiological changes similar to those induced by a-neurotoxins have been observed, as well as presynaptic effects (Parmentier and Carpenter, 1976;Vital Brazil and Fontana, 1983, 1984;Goularte et al., 1995). Cardiotoxic, haemolytic and myotoxic activities have been reported also (GutiCrrez et al., 1980(GutiCrrez et al., , 1983(GutiCrrez et al., ,1986(GutiCrrez et al., ,1992Tan and Ponnudurai, 1992). The major obstacle to study Micrurus venoms is the small quantity of material that can be collected (BolanBs, 1972). Thus, the biochemistry and the pharmacology of components isolated from coral snake venoms are not well documented. After the first attempts to purify venom proteins (Ramsey et al., 1971), only two phospholi- et al., 1979;Arroyo et al., 1987). More recently, a comparative chromatography study on Brazilian coral snake venoms has been conducted (Da Silva et al., 1991). From an immunological point of view, Micrurus and other elapid venoms contain some crossreacting components (Minton, 1979;Alape-Girbn et al., 1...