The presence of mast cells in the subepithelial connective tissue of the human endolymphatic sac has, to the best of our knowledge for the first time, been described. A hypothesis has been put forward in which these cells, which are known to contain histamin, heparin and serotonin, play an important role in the physiologic functions of the endolymphatic sac as well as in some pathologic states of the inner ear.