Olfactory dysfunction consists of conductive olfactory dysfunction, sensorineural olfactory dysfunction, and central olfactory dysfunction. Conductive olfactory dysfunction can be improved by nasal steroids and/or endoscopic sinus surgery. On the other hand, there is no effective treatment for sensorineural olfactory dysfunction. Therefore, the use of regenerative medicine for sensorineural olfactory dysfunction was investigated. To improve sensorineural olfactory dysfunction, it is essential that olfactory cell regeneration and re-synaptogenesis with originally-innervated upper neurons in the olfactory bulb glomerulus. These problems were examined using bone marrow transplantation and a traumatic head injury model. Although the potential of regenerative medicine for olfactory cells using bone marrow cells has been shown, reconstructing correct synapse formation in the olfactory bulb is a difficult problem to be solved.