We evaluated the efficacy and toxicity of aclarubicin for acute non-lymphocytic leukemia (ANLL) refractory to daunorubicin in childhood. Twenty-four patients were treated with aclarubicin and prednisolone with or without 6-mercaptopurine and behenoyl-cytosine arabinoside daily for 5 to 14 days. Of 21 evaluable patients, 14 (67%) responded: 12 obtained complete remission and 2 partial remission. The median time to reach complete remission was 37 days (range, 16 to 60 days), and the median duration of complete remission was 5.5 months (range, 2 to 41 months). The cumulative dose of anthracycline administered before the study was not considered significant for the response. The only major complication was severe bone marrow suppression; infectious episodes occurred in 14 patients (58%) and three died of sepsis and/or bleeding. The observed non-hematologic toxicities included hematuria, an elevation of serum amylase, nausea/vomiting, and angitis. In addition, one patient showed abnormal cardiac function. Aclarubicin is therefore considered a highly active drug for remission reinduction of previously treated children suffering from ANLL with an acceptable toxicity.