Monocytosis, occurring in the majority of sarcoidosis cases in the bloodstream, and an increased number of natural killer cells are a manifestation of an increased cellular defence by bone marrow cells. The antigen-offering function of natural killer cells, macrophages and monocytes, should be specially emphasized. While the majority of sarcoidosis patients show an absolute lymphocyte count of less than 1500 cells/microliter during the usual clinical blood tests, the determination of lymphocyte subpopulations by means of monoclonal antibodies displayed a different behaviour of the lymphocyte subpopulations, especially a substantial reduction of T-cells, while B-lymphocytes were at normal levels. The assumption, that sarcoidosis immunology is characterized by an imbalanced homeostasis in the sense of a decrease in cellular and an increase in humoral immune defence, can no longer be maintained. We are rather dealing with an increased immunological activity of the cellular and humoral immune defence. In addition, the investigation of the lymphocyte subpopulations in the blood allows a judgement on the existing activity of the disease. The statement of a helper-suppressor ratio of less than 2.0 suggests progress of disease and indicates therefore drug therapy. Our immunological findings also explain the difference of the prognosis, which is more favourable for women than for men.