The role of the different epithelial compartments during degeneration and regeneration of the rat prostate is examined on basis of intermediate filament protein (IFP) expression pattern. With the monoclonal antibodies RCK 103 and RGE 53, directed against specific keratins, it was possible to differentiate between the basal (RCK 103+) and luminal (RGE 53+) cells of the prostatic epithelium. After testosterone deprivation, by orchiectomy, an extensive and rapid cell loss was observed which appeared to affect mainly the luminal cells. In the process of prostate regeneration, induced by testosterone administration, using silastic implants, the luminal compartment rapidly regained its normal thickness. A heterogeneous population of morphologically luminal cells was observed showing keratin expression patterns intermediate between basal and luminal cells. These findings support the idea of a relationship between basal and luminal cells as being members of the same lineage of differentiation.