A multicentric prospective pilot study using three different schedules of high-dose Ara-C at dosage of 3 g/m2 every 12 hours during 3 h of infusion was undertaken by the Italian Cooperative Group GIMEMA in order: 1. to evaluate the safety and efficacy of such treatment in previously untreated ANLL patients more than 50 years old; 2. to investigate whether the addition of a standard maintenance treatment after consolidation with 4 courses of DAT (Daunorubicin + Ara-C + 6-Thioguanine) could improve the duration of complete remission (CR) and the proportion of long-term survival. Overall 43/125 evaluable patients (34.4%) achieved CR. 32/125 died during the induction phase, the remaining 50 patients (40%) failed to achieve CR. As for the toxicity, the most significant toxicity of all schedules was hematologic. No substantial neurological or cardiac toxicity was observed. The multivariated analysis of several pretreatment characteristics revealed that age more than 60 yr, male sex and presence of infections at diagnosis were the most significant adverse factors for achievement of CR. The median duration of DFS for all responders was 9 months, with relapse-free survival at 4 yr estimated at 29%. The addition of maintenance treatment to consolidated patients had no advantages in respect to the control group, even though the statistical analysis revealed a p = 0.058. However, because of the small number of randomized patients, no conclusions can be drawn concerning the importance of maintenance treatment.