Testosterones have beneficial effects not only on the modulation of expression of autoimmunity of B/W mice, but on other unrelated models such as autoimmune thyroiditis as well. This study was performed to evaluate the effect of testosterone in the treatment of immune-mediated sensorineural hearing loss (IMSNHL). To induce IMSNHL, 29 female Wistar rats were sensitized with bovine inner ear antigen three times weekly. Fourteen of 29 rats were injected subcutaneously three times a week with 250 microg of testosterone propionate from 1 week prior to the first sensitization to 1 week following the second booster sensitization. An auditory brain-stem response (ABR) test was performed prior to each antigen challenge and at 1, 2, 3, 4, 6 and 8 weeks following sensitization. On ABR testing, the testosterone-treated animals showed better results than the control animals with IMSNHL in the degree of hearing loss (10 to 20 dB vs. 10 to 40 dB) and incidence of hearing loss over 20 dB (25.0% vs. 53.3%). None of testosterone-treated animals showed a hearing loss over 20 dB, whereas 40% of the control animals with IMSNHL revealed hearing loss over 20 dB. These results suggest that testosterone propionate may be effective in the prevention of and early recovery from IMSNHL and may be used in the future as a one treatment modality for IMSNHL.