Fifty two adults (aged 15 to 66 years) with newly diagnosed acute lymphoblastic leukemia (ALL, n = 47) or lymphoid blast phase chronic myelogenous leukemia (Ly-CML, n = 5) were managed with three distinct protocols containing idarubicin at a cumulative dose of 36, 20, and 10 mg/m2, respectively, plus vincristine, L-asparaginase, and prednisolone (IVAP-1, -2, -3). IVAP-1 was highly toxic and gave a low complete remission (CR) rate (7/17, 41%). Nine patients died of complications while severely neutropenic, and one had resistant disease. In contrast, 24 of 28 patients subsequently treated with IVAP-2 achieved a CR (86%, p 0.005), the rate of both hematological and extrahematological toxicity being significantly reduced compared with IVAP-1 (p < 0.05). With IVAP-3, 6/7 patients aged > 60 years achieved CR. IVAP-2 with total idarubicin 20 mg/m2 is a very effective and well tolerated regimen for the initial treatment of adults with ALL.