Apparatus for inactivating renal nerve conduction at a renal artery in a mammalian subject, the apparatus comprising: an ultrasound transducer that is tubular and has an axis, and is adapted for insertion into a renal artery of the mammalian subject and for transmitting pulses of unfocused ultrasound energy in a 360° cylindrical pattern surrounding the axis of the transducer; and an actuator electrically connected to the transducer, the actuator being adapted to control the ultrasound transducer to transmit unfocused ultrasound energy into an impact volume of at least 0.5 cm 3, encompassing the renal artery so that the unfocused ultrasound energy is applied at a therapeutic level sufficient to inactivate conduction of renal nerves throughout the impact volume, the apparatus further comprising a catheter with a distal end and a proximal end, the transducer being mounted to the catheter adjacent the distal end, the catheter and transducer being constructed and arranged to allow a substantial flow of blood through the renal artery while the ultrasound transducer is positioned within the renal artery, wherein the catheter is constructed and arranged to hold the transducer out of contact with the wall of the renal artery with the axis of the transducer generally parallel to the axis of the renal artery, wherein the catheter includes a centering element in proximity to the transducer, the centering element being arranged to hold the transducer substantially centered in the renal artery, the centering element including an expansible element, namely a balloon characterised in that the balloon has a partially non-circular profile (80, 82) that is adapted to engage the wall of the renal artery without substantially blocking flow of blood through the renal artery, the balloon being formed from a porous membrane or with holes, such that cooled liquid being circulated within the balloon may escape or be ejected from the balloon; and in that the actuator incorporates a control board and a reader for reading a machine-readable element that the control board may use to set the appropriate frequency for exciting the transducer, wherein the machine-readable element is located on the transducer. an ultrasound transducer that is tubular and has an axis, and is adapted for insertion into a renal artery of the mammalian subject and for transmitting pulses of unfocused ultrasound energy in a 360° cylindrical pattern surrounding the axis of the transducer; and an actuator electrically connected to the transducer, the actuator being adapted to control the ultrasound transducer to transmit unfocused ultrasound energy into an impact volume of at least 0.5 cm 3, encompassing the renal artery so that the unfocused ultrasound energy is applied at a therapeutic level sufficient to inactivate conduction of renal nerves throughout the impact volume, the apparatus further comprising a catheter with a distal end and a proximal end, the transducer being mounted to the catheter adjacent the distal end, the catheter and transducer being constructed and arranged to allow a substantial flow of blood through the renal artery while the ultrasound transducer is positioned within the renal artery, wherein the catheter is constructed and arranged to hold the transducer out of contact with the wall of the renal artery with the axis of the transducer generally parallel to the axis of the renal artery, wherein the catheter includes a centering element in proximity to the transducer, the centering element being arranged to hold the transducer substantially centered in the renal artery, the centering element including an expansible element, namely a balloon characterised in that the balloon has a partially non-circular profile (80, 82) that is adapted to engage the wall of the renal artery without substantially blocking flow of blood through the renal artery, the balloon being formed from a porous membrane or with holes, such that cooled liquid being circulated within the balloon may escape or be ejected from the balloon; and in that the actuator incorporates a control board and a reader for reading a machine-readable element that the control board may use to set the appropriate frequency for exciting the transducer, wherein the machine-readable element is located on the transducer.