This paper describes a palaeomagnetic study of the Cygnet syenite boss, associated dykes, hybrid rocks, and baked sediments, giving new information relevant to the age of the intrusion. All these groups have parallel directions with a steep negative inclination, except those somewhat affected by a commponent induced by the earth's present field. The latter component has been minimized by treatment in alternating magnetic fields and the resulting directions, which are parallel to those in the Tasmanian dolerite, are interpreted as being the direction of the earth's field at the time of cooling. This suggests that the Cygnet intrusions are probably closely related in time to the Tasmanian dolerites, as Carey (1958) has argued from structural considerations.