Changes of rat inner ear de novo protein synthesis in response to dexamethasone (DEX), a synthetic glucocorticoid, have been analyzed by high resolution two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (2D-SDS-PAGE) and fluorography. Two proteins (Mr 41 000 and 35 000) were amplified and one protein (Mr 47 000) was suppressed by DEX in a cochlear culture medium. In the culture medium conditioned by vestibular tissue, three proteins (Mr 67 000, 57 000 and 50 000) were amplified after DEX administration. In cochlear and vestibular tissues, glucocorticoid-responsive protein synthesis was down-regulated by DEX, including two proteins (Mr 39 000 and 35 000) in the cochlea and five proteins (Mr 80 000, 64 000, 59 000, 56 000 and 40 000) in the vestibule. The regulation of these inner ear proteins by DEX suggests that glucocorticoid may play an important role in normal inner ear microhomeostasis, as well as in the treatment of some inner ear disorders. © 1995.