A neurotoyin, Oh9-1, from the venom of Ophiophagus hannah was isolated by a combination of ion-exchange chromatography and reverse phase HPLC. Amino acid sequence analysis revealed that Oh9-1 consists of 57 amino acids and eight cysteine residues, This protein was mainly constituted with beta-sheet as evidenced by CD spectrum. Oh9-1 inhibited carbachol-induced muscle contraction in an irreversible manner and the dose for achieving 50% inhibition was approximately fourfold that of alpha-bungarotoxin. Since the residues in alpha-neurotoxins closely involve in the binding with acetylcholine receptors are not highly conserved in this toxin molecule, Oh9-1 represents a novel type of neurotoxin structurally distinct from alpha-neurotoxins. (C) 2002 Elsevier Science (USA). All rights reserved.