255 patients with acute non-lymphoid leukaemia (ANLL), observed between October 1984 and June 1987, entered a chemotherapy regimen consisting of induction therapy with cytarabine in combination with idarubicin (IDA/ARA) or daunorubicin (DNR/ARA), followed by consolidation with four courses of IDA + ARA plus 6-thioguanine (6-TG) or DNR + ARA + 6-TG and a 6 month maintenance therapy with 6-TG and ARA. The median age was 62 years (range 55-78 years) and 33 were aged more than 70 years. The treatment groups were comparable for median age, FAB type, performance status and initial blood counts. 249 patients were randomised, 124 to the IDA/ARA arm and 125 to the DNR/ARA arm. Complete remission was achieved in 50 patients (40%) on the IDA/ARA treatment program and 49 patients (39%) on DNR/ARA. No definite differences were found between patients receiving IDA/ARA and those treated with DNR/ARA as far as complete response (CR), overall survival, failure free and relapse free survival are concerned. 74% of the complete responders in the IDA/ARA arm and 51% in the DNR/ARA arm achieved CR after a single course of treatment. Resistant leukaemia was observed in 13.7% of the patients in the IDA/ARA arm and in 31.2% in the DNR/ARA one, whereas hypoplastic death occurred in 29% and 14.4%, respectively. In conclusion, our data failed to show any advantage of idarubicin over daunorubicin even though there is some evidence that IDA, despite the higher toxicity, is more rapid in eradicating leukaemia as proved by the higher CR rate obtained after one course of induction.