A sound-attenuating ventilation louver is provided for location in an aperture of a wall which separates a chamber containing a source of noise from the external environment, the purpose of the louver being to allow gaseous flows to pass into and out of the chamber while minimizing the noise passing out through the louver from the noise source. The louver includes a plurality of profiled slats each in the form of an aerodynamically-shaped blade. Each slat includes a solid portion made of a sound-absorbent material and a hollow portion defined by a thin wall of rigid material; in use of the louver the sound-absorbent solid portion of each slat is disposed towards the chamber containing the noise source while the hollow portion is disposed towards the external environment. The hollow portion of each slat is subdivided into a plurality of chambers communicating with the atmosphere through ports and acting as resonators.