The anti-leukaemic effect of low-dose cytosine arabinoside was assessed in 36 patients; 15 patients presented with an acute myeloblastic leukaemia and were treated in first induction because of age or preexisting disease and clinical and biological stabilization was obtained in 7 cases, with a mean duration of 8.7 months. In 4 relapsed patients 2 complete remissions were obtained, 1 of which after several courses of cytosine arabinoside. In all cases an important haematopoietic and extra-haematopoietic toxicity was noticed. In 15 patients treated for a myelodysplastic syndrome terminating in acute myeloblastic leukaemia stabilization was obtained in 8 cases, but final conclusions were difficult. The cytotoxic effect of cytosine arabinoside even at low dosage remains important. The optimal modalities in the administration, and the actual advantages of this treatment compared with conventional chemotherapy have still to be defined.