Based on a series of clinical and laboratory studies of leukemia cell kinetics and responses to chemotherapy, we have developed an intensive timed-sequential regimen of daunorubicin and high-dose infusion 1-beta-D-arabinofuranosyl cytosine for the treatment of adult acute nonlymphocytic leukemia. Of the first 34 patients achieving complete remission (CR) with a single cycle of this therapy, four (12%) remain in complete remission without further therapy after a minimum of five years of follow-up. Treatment of relapsed patients with a second course of the same regimen at relapse and no chemotherapy in second remission increased to seven (21%) the number of patients expected to remain in remission for four years or more from their last chemotherapy. Beginning in 1980, however, we gave all consenting adults a second cycle of this chemotherapy in early first remission. Of the first 25 patients treated with a second cycle of this chemotherapy in early first remission, there was one toxic death, but 11 patients (44%) remain in CR with a median follow-up of almost three years.