A microwave applicator comprising a coaxial electrical input (4) and a waveguide (1) filled with dielectric (2), an inner conductor (7) of the coaxial input extending longitudinally within one end of the waveguide to launch microwaves in the TM01 mode to travel to the distal end face (8) of the waveguide so that microwaves are transmitted when the distal end face is contacted by the biological tissue to be treated.