Repeated applications of stellate ganglion block (SGB) are known to improve symptoms of allergic rhinitis but the mechanism of the effects is not clear. Correlation between nervous system and immune system has been reported. To examine if the blockade of a part of the sympathetic nervous system like SGB could affect immune system activity of whole body, YAC 1 cell lytic activities of the splenic natural killer cell (NK activity) were compared between the sham operation group (n = 12) and the cervical sympathetic denervation group (n = 10) 4 weeks after the operation. NK activity of denervation group was significantly lower than that of sham group. The result suggests the possibility of modulation of the immune activity of individuals by partial blockade of the sympathetic nervous system.