Cell mediated immunity in the respiratory tract, operating somewhat independently of systemic cell mediated immunity CMI, has been recognized only rather recently. Local CMI has been shown to be more consistently and more potently stimulated following local administration of immunogen. In addition, in the few studies that have been done relative to protection, local immunization has resulted in greater resistance to organisms usually considered protected against by CMI. Thus, like the humoral immune system, CMI appears to operate locally in the respiratory tract, at least partially independent of systemic CMI. This paper deals with the evidence relative to local CMI, as well as a discussion of the role of the pulmonary macrophage, the mechanisms whereby local CMI may operate in protection, and the evidence for the presence of T-cell memory in the respiratory tract.