A microwave applicator having a probe which comprises an elongate shaft (14), the shaft having an external tubular wall (18), a radiating portion (15) disposed at the distal end of the shaft (14), a transmission line (17) extending to the radiating portion internally of the tubular external wall (18), and an elongate flow dividing member (19) which co-extends with the transmission line (17) longitudinally of the shaft (14), the side wall of the transmission line (17) and the side wall of the flow dividing member (19) contacting each other and contacting the internal surface of the external tubular wall (18) at two-spatially separated discrete positions, thereby defining a pair of flow channels (20, 21) inside the shaft (14). In use, cooling fluid can pass down one channel (20) and return via the other channel (21). The structure of the probe is uncomplicated and the probe is straightforward to assemble.