Immunopathology of olfactory mucosa following injury to the olfactory bulb. Removal of the olfactory bulb was performed on rats in an attempt to elucidate the processes of olfactory dysfunction following head injury. Degeneration and regeneration of the olfactory mucosa were examined, histopathologically and immunohistochemically. We used antisera to olfactory marker protein (OMP) and neuron specific enolase (NSE) as a marker of the mature olfactory receptor neurons. Following rapid degeneration after bulbectomy, the olfactory receptor neurons regenerated. OMP and NSE containing cells re-appeared 49 days later. However, the cell population of the neuroepithelium did not revert to the numbers observed in the non-operated neuroepithelium, even three months later. The lack of a connection between regenerated axons and the olfactory bulb may result in immature neuronal replacement and reduce the number of olfactory receptor neurons. 