From October 1993 to December 1994, 26 patients with newly diagnosed and untreated acute nonlymphocytic leukemia (ANLL) received induction chemotherapy with the 3 + 7 regimen, i.e., idarubicin (IDA) 12 mg/m2/d for 3 days any cytosine arabinoside (Ara-C) 100 mg/m2/d for 7 days. Complete remission (CR) was achieved in 80.8% of the whole group and in 66.7% (two of three) of the elderly subgroup (age > or = 60 years). Seventeen patients achieved a CR after only one course, whereas four needed two courses. Toxicity was tolerable. All of the patients experienced myelosuppression, and infection episodes were noted in all except one patients. Other toxicities included vomiting (62%, mostly mild to moderate, grade I/II), diarrhea (46%, mostly grade I), mucositis (65%, mostly grade I), and alopecia (100%). None presented with liver dysfunction or cardiotoxicity. Of the 21 complete responders, one refused further consolidation, 20 received either two additional courses of IDA/Ara-C or high-dose Ara-C as consolidation, and one died of infectious complications during consolidation. As of May 1995, nine had relapsed, and 11 (55%) continued in CR for 6 to 21 months (median, 14.5). All four patients who needed two courses of IDA/ Ara-C to achieve remission had relapsed, with either high-dose Ara-C or allogeneic bone marrow transplantation (BMT) as postremission therapy. We suggest that induction failure with one course of IDA/Ara-C is a poor prognostic factor in ANLL.