The κ-neurotoxins are a small group of proteins belonging to the 'α-bungarotoxin' family of proteins derived from the venom of elapid and hydrophid snakes. They are related by their amino acid sequence similarity as well as their three dimensional structure. Members of this family include the κ- and α-neurotoxins, muscarinic toxins, cytotoxins, cardiotoxins, fasciculins, calciseptins and mambins. Like the α-neurotoxins, κ-neurotoxins bind to and inhibit nicotinic acetylcholine receptors but are distinguished from the α-neurotoxins by their receptor specificity and differential binding kinetics. κ-Neurotoxins are also distinguished by their ability to form dimers in solution at physiological concentrations. The available evidence suggests that the dimer nature of κ-neurotoxins plays a role both in the mechanism by which their polypeptide chain folds to produce the mature toxin as well as potential involvement in their interaction with their respective receptors.