Abstract
A case suffering from a so-called pure monocytic leukemia displayed excessive monocytic hyperproliferation, moderate histiocytic infiltrations in lymph nodes and liver, hyperproliferation of plasma cells and monoclonal hypergammaglobulinemia of the IgG type. Monocytic cells proved to be normal with respect to morphology including electron microscopy, cytochemistry, capacity of phagocytosis, motility and differentiation potential. An increased fraction of immature monocytic cells gained access to the blood. The immature cells being able to egress from the marrow proved incapable to leave the microcirculation. They continued to circulate until completion of differentiation to mature monocytes which finally developed a normal emigration potential.