The invention relates to a powder inhaler operating on the Bernoulli principle with replaceable cylindrical disposable capsules as the active substance reservoir. The powder inhaler consists essentially of a preferably cylindrical capsule chamber provided with means for laterally opening the capsule, an air inlet opening in the capsule chamber and an air outlet opening and a mouthpiece mounted downstream of the air outlet opening. The capsule chamber is constructed so that after insertion the reservoir capsule can essentially only move in the longitudinal direction when a sufficiently powerful air stream passes through the capsule chamber, guided substantially parallel to the longitudinal axis of the capsule. According to the invention, the inner wall of the capsule chamber is uneven in order to achieve a better emptying of the capsule than is obtained with a smooth inner surface.