In the late stages of inner ear development, the relatively undifferentiated cells of Kollicker's organ are transformed into the elaborately specialized cell types of the organ of Corti. Microtubules are prominent features of adult cells in the organ of Corti, particularly supporting cells. To test the possible role of microtubules in organ of Corti development, the microtubule organization in the organ of Corti has been examined using indirect immunofluorescence to beta-tubulin in the developing gerbil cochlea. Tubulin first appears at post-natal day 0 (P0) as filamentous asters in inner hair cells and by P2, asters are also seen in outer hair cells. Tubulin appears at P3 in inner pillar cells in a tooth crown-like figure. By P6, tubulin expression is also evident in outer pillar cells and by P9, it is seen in Deiters cells. Elaboration of microtubules in pillar cells was observed to proceed from the reticular lamina towards the basilar membrane. The pattern of tubulin expression in the apical organ of Corti lags the base by about 3 days until P6, but by P9, apical and basal organ of Corti appear substantially the same.