Ten patients either in relapse (n = 7) or refractory (n = 3) acute leukemia were treated with high-dose Ara-C (3000 mg/m2) every 12 hours to a total of eight 2 doses (24,000 mg/m2). Myeloblastic (n = 5), lymphoblastic (n = 4) and hybrid (n = 1) acute leukemias were included. In the total group, complete remission was achieved in 6 of 10 cases (60%); the remission rate was higher in the relapsed than in the refractory acute leukemia group (71 versus 33%;) the duration of the complete remission ranged between 1 and 13 months, with a median of 2 months; the remission duration was also higher in the relapsed than in the refractory acute leukemia group (4 versus 1 month). Refractoriness to the high-doses of Ara-C was observed in two cases, and fatal iatrogenic myelosuppression was produced in two patients. The rate of complete remission was 80% in myelogenous leukemia and 50% in lymphoblastic leukemia. It is concluded that high-dose Ara-C is another therapeutic choice in the treatment of relapsed and perhaps refractory acute leukemia.