Dr. HEIMPEL asked Dr. SCHMALZL about the special contribution of cytochemistry to the prognostic security of his patients: in his own experience, a large number of the so-called preleukemias die before developing acute leukemia; these patients are not mentioned in the tables. Dr. SCHMALZL answered that the contribution of the cytochemical examination consists in the more accurate identification of maturative defects in the blood and the bone marrow cells, which cannot be achieved by conventional morphologic examination. Although these defects are not strictly specific for preleukemia, it must be emphasized that maturative, proliferative, and cytogenetic parameters are, at present, the only criteria which permit the identification of preleukemic disorders. The high diagnostic sensitivity of the cytochemical examination can corroborate the clinical suspicion of preleukemia at an early stage of the disease and should induce further appropriate, cytogenetic and cultural investigations. According to the authors the latter tests became diagnostic at a later stage of the disease.