A microwave applicator device comprising a probe (11) for ablating the body of a human or animal, a cooling passage (20,21) extending through the probe (11) and arranged to carry a cooling fluid, a pump (71) for pumping the fluid through the probe (11), and an elongate flexible duct (104) extending between the pump (71) and one end of the cooling passage (20,21), the pump comprising a pump body (73) including a motor (120) and a pump head (72) detachably mounted to the pump body (73), the pump head (72) comprising a first port (86) connected to a proximal end of the elongate flow duct (104), a second port (85) and fluid propulsion means (84,92) for creating a flow of fluid between the ports (85,86) and along the elongate flow duct 104 upon energisation of the motor (120), the pump head (72) being arranged to sealingly contain the fluid. The pump head (72), the elongate flexible duct (104) and the probe (11) form a replaceable assembly that can be detached from the pump body (73) and discarded following use.
