During the examination of a large number of Army personnel for defects of hearing, the following problem arose: Patients were being seen who complained of deafness of varying degrees, with a normal history and with examination of the external ear, ear canal and ear drum presenting normal results. They had been given diagnoses of defective hearing of undetermined cause; yet a cause should be discoverable if looked for. The question was where to look. Histories obtained from these patients contained no references to previous aural complaints, except for deafness, which usually had been present since infancy or early childhood. In 1 case, a history of a fall in childhood was reported, but there was doubt that this could be a causative factor for the patient's deafness. In view of these negative observations and of the fact that the men had normal-appearing ear drums, roentgenograms of the mastoids were ordered, and