Crude extracts from hypobranchial glands of two species of muricid gastropods, Thais clavigera and Thais bronni, were highly lethal to mice. Regardless of species, a new choline ester was isolated as the major toxic principle and elucidated to be tigloylcholine, a structural isomer of senecioylcholine widely found in gastropod hypobranchial glands, by 1H- and 13C-NMR as well as FAB-MS. The i.v. LD50 (mouse) of tigloylcholine was estimated to be 0.92 mg/kg.