Expression of mRNA for pituitary adenylate cyclase-activating polypeptide (PACAP) was detected in the cochlea of rats using a reverse transcription-polymerase chain reaction and in situ hybridization. Examination of in situ hybridization demonstrated that cells in the spiral ganglion, and marginal cells in the stria vascularis expressed mRNA for PACAP. These findings suggest that PACAP may play an important role in regulating cochlear functions.