The reaction of the body to inhaled mineral dust brings into play physiological and pathological mechanisms in which immunological processes may be involved. An analysis is made of phagocytosis by alveolar macrophages, of the transport of dust to the lymphatic system, of dust aggravation in lymphoid tissues on lymph glands and of the resulting lesions. The part played by dust in immunological disturbances is put forward in the cases of tubercular infections, experimental arthritis and tumors.