Venoms from Micrurus (New World coral snakes) display potent peripheral neurotoxicity which may cause death by respiratory paralysis, yet many are poorly or not characterized. The major venom components of coral snakes are three-finger toxins (3FTxs) and phospholipases A2, whose proportions vary among species. As a trend, venoms of Micrurus from South America contain high proportions of 3FTxs, in contrast to most North and Central American species. Micrurus tschudii tschudii, the ‘Desert coral snake’ from Perú, displays an extreme 3FTx-predominant venom phenotype, with ∼95% of its proteome belonging to this protein family. This study evaluated the toxicity of its major 3FTxs in mice. A lethal 3FTx, here named tschuditoxin-I, was purified and sequenced by MALDI-TOF-TOF and N-terminal degradation. Tschuditoxin-I showed highest similarity to MS-1, a short-chain α-neurotoxin from the aquatic, fish-eating coral snake M. surinamensis. The single amino acid substitution between these two toxins maps at the tip of the first β-stranded ‘finger’ in the modeled structure of tschuditoxin-I, suggesting it may have a role in interaction with its target, which remains to be investigated. Owing to its lethal action, tschuditoxin-I is likely to be medically relevant in envenomings. In spite of its 74% sequence identity with an α-neurotoxin of M. nigrocinctus, an equine antivenom raised against venom of the latter did not immunorecognize tschuditoxin-I or M. t. tschudii venom by ELISA. This underscores the need of characterizing the biochemical and immunological properties of the main toxic components of Micrurus venoms, aiming to improve the limited para-specific coverage of current antivenoms.