CFU-L is considered as the clonogenic cell of acute non-lymphoblastic leukaemias (ANLL). Twenty-five malignant myelogenous hemopathies (5 blast crisis and 20 "de novo" ANLL) were studied in order to assess the proliferative capability of these cells and its relationship to FAB types and the achievement or not of complete remission (CR). The proliferative capability was assessed by culture on methylcellulose using conditioned leucocyte medium stimulated with phytohaemagglutinin as stimulating agent. Cell proliferation was observed in 21 cases, reaching 100% of the blast crisis and 80% (i.e., 16 cases) of the "de novo" ANLL. As regards the FAB types, it was found that the leukaemias with monocytic cells showed higher cell-growth than those of granulocytic lineage (90%, vs 60%). Of the patients not achieving CR (12 cases) colonies were formed in 66.6% (8 cases), while of the 8 patients who attained CR only in 3 (37.5%) were colonies observed. It was concluded that the FAB types of ANLL show different proliferative capability, which might influence the prognosis of the disease.