The dominant and sex-linked forms of hereditary hearing loss, which have long been recognized, are readily identified on the basis of the family history and routine hearing tests. The mode of inheritance of the recessive forms of hereditary deafness, on the other hand, has been extremely difficult to determine. The research of the last few years, however, has disclosed that carriers of genes for recessive deafness can be identified by audiometric recording of certain peculiarities in the hearing function. This is an important advance, not only as regards diagnositc work, but also in the research into the genetics of deafness.