Abstract: A drainable blade louver comprises a pair of spaced-apart vertical members supporting a multiplicity of elongated, horizontally extending, inclined blades, each of which is of uniform cross section along its length. Each blade has an upwardly open front drainage trough located adjacent the front edge of the blade and at least one second upwardly open drainage trough located in at least about the front one-third of the blade closely adjacent the front trough. Each of the troughs is defined by spaced-apart front and back walls, the upper edges of which are preferably located in a plane substantially parallel to the airflow streams passing between the blades, and a bottom wall spaced a substantial distance below the upper edges of the front and back walls such that the splash from water drops impinging on the bottom walls of the troughs is largely confined to the zone bounded by the walls of the troughs thereby minimizing entrainment of water in the airflow streams.