RESUMEN
The occurrence and ultrastructure of the so-called "labyrinths" were investigated in the bone marrow cells from 13 patients with preleukaemia and acute leukaemia. Except for one patient, labyrinths were found in the myeloid cells from patients with preleukaemia and acute myelogenous leukaemia. Labyrinths could not be detected in lymphoblasts from patients suffering from acute lymphoblastic leukaemia or in plasma cells from a patient with plasma cell leukaemia. In patients with preleukaemia and smoldering leukaemia, labyrinths could be detected in all differentiation forms, from myeloblasts to mature polymorphonuclear granulocytes. Since it is improbable that labyrinths develop in consequence of exogenous effects, their presence in the mature granulocytes points to the in vivo maturational ability of leukaemic precursors in certain cases of acute myelogenous leukaemia and preleukaemia.
