Fimbrin is an actin-binding protein that organizes actin filaments into parallel bundles. We have used fluorescence immunocytochemistry and confocal laser scanning microscopy to demonstrate that the detection of fimbrin in the chicken basilar papilla (BP) by this method was limited to the hair cells. These experiments indicate that it was concentrated in the bundles of stereocilia. In addition, there was no evidence for the presence of fimbrin in the supporting cells, border cells, or hyaline cells. During recovery of the BP following acoustic trauma, the appearance of fimbrin in regenerating hair cells was first seen approximately 96 h after the onset of the sound exposure. This was the time at which new hair cells first appear in the BP. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect transcription of the fimbrin gene in both control and sound-damaged BP. Semiquantitative RT-PCR indicated no detectable changes in fimbrin transcription levels 2 or 5 days after the onset of pure-tone exposure. These data indicate that fimbrin can be used immunocytochemically as a hair-cell-specific marker during regeneration in the chicken cochlea.