Manually actuable inhaler (1) for pulverulent substances, during manual actuation, apportions a defined discharge quantity (20′) from a substance storage quantity (20) in a metering chamber (D) upstream of a discharge passage (21), for providing an airborne. discharge from a mouthpiece opening (14). The inhaler has a piston (8) which generates the discharge airstream, together with a cavity (17) in a body portion (15) of the piston, the cavity forming a substance storage chamber (SV) and the metering chamber (D). A reduced pressure, which is generated during a return stroke of the piston (8), opens the metering chamber (D) toward the substance storage quantity (20). The base of the metering chamber (D), is formed by an air-permeable membrane and the chamber is closed by a valve cone (65).