The effect of low-dose Ara C (LD-Ara C) (10 mg/m2 q 12 hr s.c.) for a minimum of 10 days was evaluated in 21 patients with acute myeloid leukemia (AML) and 15 patients with dysmyelopoietic syndromes (DMPS). Median age (range) for AML-patients was 47 yrs (19-89), and for DMPS-patients 60 (22-78). From the AML-group, 9 patients were either primary refractory or resistant to intensive re-induction treatment of relapse, 6 others had heavy pretreatment, 1 suffered from myelosclerosis. Five AML-patients had no pretreatment at first presentation and were started on LD-Ara C because of old age (3) or poor condition (2) including 1 patient with a secondary leukemia. DMPS included those with RAEB (8) and RAEB in transformation (7). 12 patients with AML and 4 with DMPS displayed a leukocytosis of greater than 10 X 10(9)/l. Three out of 21 AML-patients reached complete remission (CR), one of them twice, with partial remission (PR) at the third attempt with this type of treatment. Two other AML-patients reached a P.R. of 5 and 1 months duration respectively. Three patients experienced a transient response characterized by improved peripheral blood counts and cessation of transfusion requirements, one of them for 12 months. In 5 AML-patients no effect was seen and 8 pts. died. In the DMPS-group, 5/15 patients reached C.R., one patient twice with the same treatment, 1 patient reached a P.R., 1 improved, 6 showed no effect, and 2 died. In 13 patients final examination of the bone marrow was not performed after treatment because of either early death or obvious progression. Treatment was associated with significant, transient hematologic toxicity. Patients suffering from DMPS had prolonged aplasia and required more blood and platelet support than pts with AML. Responding leukemia patients had a rapid hematologic regeneration. Considering the poor prognosis of both of our treatment groups, this therapeutic approach proved to be of considerable benefit.