A total of nine adults with newly diagnosed acute myeloblastic leukaemia (AML) and seven with relapsed disease were treated with fractionated daunorubicin in combination with cytosine arabinoside and 6-thioguanine. Remissions were seen in 89% and 57%, respectively. The side effects associated with bolus injections of daunorubicin were much less severe with fractionated treatment, and there was no significant cardiotoxicity despite total doses of up to 1363 mg/m2 daunorubicin. These results show that fractionated anthracyclines are effective in the treatment of AML and that this mode of administration may permit an upward revision of the accepted dose limits for anthracyclines.