Heat shock proteins(HSPs) are induced in cells by temperature elevation or other stressful treatment and these proteins likely play a role in cellular repair and survival mechanisms. In the peripheral auditory system several investigators have demonstrated the induction of 72 kD HSP with hyperthermia and transient ischemia and we have previously shown the noise induced HSP 72 expression in outer hair cells of the rat cochlea. Animals were exposed to 110 dB SPL broad band noise for 1.5 hours. This exposure resulted in 30-50 dB threshold shift for 3-4 hours. Animals sacrificed 6 hours after stimulation showed noise induced HSP 72 immunoreactive staining of outer hair cells and stria vascularis with no staining of inner hair cells or spiral ganglion cells. Animals exmined for scar formation using histochemical and immunocytochemical methods for actin and cytokeratin staining showed no noise induced pathology even 24 hours after exposure. HSP 72 is therefore expressed under conditions of temporary threshold shift and may be involved in protection from insults.