OBJECTIVE A randomized clinical trial was undertaken to compare the therapeutic effectiveness of idarubicin (IDR) to daunorubicin (DNR), and both were given in combination with cytarabine (CA) in acute myelogenous leukemic (AML) patients. METHODS Newly diagnosed patients were given a daily infusion of CA (100 mg/m2) for 7 days and were assigned randomly to receive DNR (45 mg/m2) or IDR (12 mg/m2) daily for the first 3 days. Those patients who achieved a complete remission (CR) were given three consolidation courses that consisted of CA (100 mg/m2 intravenously [IV]) and thioguanine (TG; 100 mg/m2 orally) every 12 hours for 5 days and either DNR (50 mg/m2) or IDR (15 mg/m2) on the first day of each cycle. After consolidation, patients received late intensification, which consisted of the same drugs used for induction except that the CA was given for 5 days and the anthracycline for 2 days. Four courses were planned at 13-week intervals. RESULTS The CR rates were 75 of 105 (71%) on the IDR arm and 65 of 113 (58%) on the DNR arm (P = .03). The median survival and median remission durations were 297 and 433 days, respectively, on the IDR arm. The median survival and median remission durations were 277 and 328 days, respectively, on the DNR arm. Six deaths occurred during late intensification, five on IDR and one on DNR; this approach was abandoned after 47 patients were entered. The median survival was significantly longer for patients who received late intensification. CONCLUSIONS This trial demonstrated that IDR was more effective than DNR in remission induction in AML.