Complex studies on the patency of the cochlear aqueduct were made on 250 human cadavers and the temporal bones isolated from these, using a chemical method (staining reaction) as well as filling the aqueduct with fluid plastics and exposing the whole of its course under an operating microscope. The disappearance of patency in the cochlear aqueduct is a progressive phenomenon reflecting the biological process of aging in the organism. Patency of the cochlear aqueduct renders possible a two-way spread of infection from the cerebrospinal fluid (CSF) to the inner ear and vice versa, CSF otorrhea, and sudden sensorineural hearing inpairment through rises in CSF pressure, while in the absence of patency, the accumulation of harmful products of metabolism in the perilymph has a deleterious effect on the sensory elements of the inner ear.