The differentiation of tissues and organs during ontogeny increases the necessity of integration of the different structures. These developmental processes of integrations by body fluids, immunologic, endocrine and nervous systems culminate in mammals, since they possess the most diversified system of body fluids. Typical of the most developed mammals are the bone marrow, the lymphatic system with regional lymph nodes and consequently the pathologic development of the diversity of leukemias, malignancies without stroma. In the German literature the leukemias are considered systemic diseases because the floating cells they discharge are more or less uniformly pathologically underdeveloped. The leukemias are named according to the major abnormal cell type (e.g. monocytic acute leukemia). Acute and chronic is the distinction of the time limitation regarding the development and duration of the disease. More complicated is the discharge of motile cells from primary tumors or daughter tumors deriving from solid tumors. These motile cells enter into the circulation via the lymphatic spaces or by penetration of the endothelium of the blood vessels. They move freely in the circulatory system until settling in a more or less distant region. The process of detecting these cells is known as carcinocythemia. Other movable cells during neoplastic progression are those populating effusions in the coelomic cavities. Non-movable, that is only growing in succession like a tissue chain are those tumors which distribute by direct tumor spread within the veins, keeping the connection with the primary tumor. This condition is especially well-known in renal cell carcinoma.(ABSTRACT TRUNCATED AT 250 WORDS)