Forty-eight patients with syphilitic labyrinthitis have been treated and followed up for periods of six months to 25 years; interpretation of the hearing results must be in the light of the natural history of this condition which is perceived to be progression of hearing loss to profound deafness. At the beginning of the series treatment was with ampicillin alone and on this treatment 11 ears with useful hearing were maintained at this level. The group with combined ampicillin and prednisone treatment, which included some failures from ampicillin alone, maintained useful hearing in 28 out of 29 ears. Those treated initially with ampicillin and prednisone and later also given regular injections of ACTH, maintained hearing in 16 out of 17 ears. At the outset, there were 29 profoundly deaf ears. One of these recovered some useful hearing but two ears with useful hearing at the outset became profoundly deaf so that at the end there were 30 profoundly deaf ears. However, all patients as opposed to ears, with useful hearing at the outset were left with some hearing; no patient became profoundly deaf.