We investigated the prognostic significance of early peripheral blast clearance as assessed by WT1 transcript reduction during the first days of standard induction therapy in 57 adult patients with acute myeloid leukemia (AML). Quantification of WT1 transcript by real-time quantitative PCR in peripheral blood on days 1 and 5 of treatment was performed. WT1 ratio was defined as the ratio of copy number measured on day 1 and on day 5. The median WT1 ratio was greater in patients attaining CR as compared to non-responders (11.68 vs. 2.14, respectively; P=0.0006). Furthermore, DFS and OS were significantly longer in patients displaying a WT1 ratio greater than 5.82 (i.e. the median value of whole cohort) than in patients with WT1 ratio of 5.82 or under (P=0.024 and P<0.001, respectively). These data suggest that early decrease of WT1 copy number in peripheral blood predicts for better outcome and should be considered in the management of AML patients.