Mucociliary function of the eustachian tube was measured with a radioisotopic method; 0.01 mL of a human serum albumin labeled with technetium 99m was instilled into the anterior part of the middle ear cavity either through a perforation or by puncturing the tympanic membrane, and its course was followed by a gamma-camera. In the normal eustachian tube, the velocity of the mucociliary transport was 0.7 to 1.1 mm/min. The mucociliary function was totally absent in chronic otitis media, in untreated secretory otitis media, and in the ear with a moist perforation of the tympanic membrane. The mucociliary transport returned to normal when the ear was clinically healed. It is assumed that the impairment of the mucociliary function of the eustachian tube and middle ear plays an important role in the pathogenesis of secretory otitis media and chronic ear discharge.