Recent evidence has provided information that the immune system can be activated by non-antigenic stimulus e.g. stress. Information on the bidirectional communication between the neuronal and immune systems has been growing, while increasing evidence suggests that neuromodulators, released from the neuronal systems, influence the immune cells. Conversely, the activated immune cells release an array of immunomodulators that influence the physiologic function of the nervous system. An attempt was made to restore the altered immune function following exposure to stress by the treatment of the olfactory system with various fragrances. From the data in experimentally designed mouse models, it was found that the individual sensitivity to the fragrances was restricted by the genetic background (H-2) of the mice. The adaptation to the fragrances with regard to the recovery of the immune response to stress, was also characterized. The ability of the adaptation to the fragrances was found to differ not only due to the genetic background of the mice but also different fragrances.