The repair process of neomycin induced cochlear damage in the postnatal developing rat was investigated in the present study. The results showed that electron dense atypical cells with a cluster of microvilli on their apical surface, resembling early stage of embryonic hair cell, were observed in the former hair cell region. The striking finding was that microglia-like cells appeared and replaced OHCs in the injured auditory sensory epithelium. Using Brdu immunohistry, cell prolifera-tion was found in the area of inner and outer spiral sulcus but not in the hair cells and supporting cells. It is proposed that microglia-like cells play a role in eliminating waste products from the organ of Corti and may participate in direct structural repair. NeuroReport 11: 1389-1393