We analyzed appearance of non transferrin bound iron (NTBI) in 30 transplant eligible patients with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) during conventional chemotherapy treatment program and evaluated possible relationship with transfusional body iron intake, iron parameters and clinical complications. For each course, serum samples for NTBI detection were taken prior to chemotherapy, during treatment and during subsequent bone marrow myelosuppression: NTBI was assessed by HPLC. Appearance of NTBI was observed from the start of induction treatment and was still detectable during bone marrow myelosuppression; the recovery of the bone marrow function coincided with the disappearance of NTBI. This kinetic was observed in all subsequent high doses chemotherapy courses, independently from confounding variables such as transfusional iron intake and transferrin saturation. NTBI seems to be a consequence of chemotherapy induced lysis of bone marrow cells and, partly, of hepatocytes after cytotoxic injury. The subsequent persistence of NTBI throughout bone marrow myelosuppression is related to the transient suspension of erythropoietic activity. Moreover, NTBI levels >2μM at the beginning of iatrogenic myelosuppression were associated with higher risk of sepsis caused by Gram negative Bacilli (RR 2.571), also compared with other infectious complications (RR 1.954).