Complete remission was achieved in a case of hypoplastic acute myeloid leukaemia with chromosomal aberration of No. 8-trisomy by giving very low dose of cytosine arabinoside (ara-C), 10 mg (7 X 5 mg/m2)/d, by 24 h continuous intravenous infusion for 20 d. We observed a definite cytoreduction phase in the bone marrow (BM) before normal haematopoiesis resumed. The remission BM showed only normal karyotypes in all metaphases examined. Granulocyte/macrophage colonies and erythroid bursts recovered sufficiently in numbers and cytogenetic study on single colonies and bursts revealed only normal karyotypes. These observations provide evidence that a low dose ara-C regimen can induce remission by cytoreduction which diverts the growth advantage from the leukaemic clone to the normal clones.