The effect of 1 percent sodium hyaluronate on the open inner ear was tested in a series of guinea pigs. By removing the stapes footplate from its original position in the oval window, direct access to the vestibule from the inner ear was achieved. The oval window niche was filled with either 1 percent sodium hyaluronate or 0.9 percent NaCl. The animals were examined with regard to both the cochlear and the vestibular partitions of the inner ear. No marked differences could be seen between the test group and the controls. Thus the organ of Corti as well as the vestibular end organs presented with normal anatomy throughout. Neither did the behavior of the animals in any way indicate any signs of inner ear disturbance. It is concluded that 1 percent sodium hyaluronate does not seem to harm the inner ear sensory structures even in the case of direct access to the vestibule as can be foreseen if the compound is used during stapes surgery.