This paper outlines the many components of the mammalian immune system and the anatomical and physiological connections suggesting that the nervous system plays a role in the modulation of immune response. The few studies attempting to measure the effect of chiropractic or manipulative treatment on the immune system are reviewed. Their results suggest that chiropractic or manipulative treatment may influence T and B lymphocyte numbers, NK cell numbers, antibody levels, phagocytic activity and plasma beta-endorphin levels. The influence of these effects on the outcome of host resistance is unknown. There is now a need for large, well-planned clinical trials using some of the more sophisticated measures of immune function to establish whether chiropractic treatment can influence the immune response in a clinically significant manner.