Transfusion-associated iron overload is often observed in patients with haematological malignancies. We analysed the effect of iron overload, indicated by high serum ferritin level, on the mobilization of CD34(+) peripheral blood stem cells (PBSCs). We evaluated the association between the serum ferritin level prior to PBSC collection and the number of CD34(+) cells collected through leukapheresis in 51 patients with various haematological malignancies. Patients with serum ferritin level over 1000 ng mL(-1) were defined as high-ferritin group. Comparing the good (> or =1 x 10(6) per kg CD34(+) cells) and poor (<1 x 10(6) per kg CD34(+) cells) mobilizing groups, there was no difference in disease status, previous chemotherapies and white blood cell count at the first day of apheresis. However, there was a significant difference in the median units of red blood cell transfused between the good and poor mobilizer (2 vs. 8 units; P = 0.012). Serum ferritin level was notably higher in the poor mobilizer (1670 +/- 1320 ng mL(-1)) compared with the good mobilizer (965 +/- 705 ng mL(-1), P = 0.035). The cumulative number of CD34(+) cells per kg collected during the whole procedure was significantly lower in the high-ferritin group (5.5 +/- 4.7 x 10(6) per kg vs. 13.1 +/- 9.1 x 10(6) per kg, P = 0.01). Multivariate analysis revealed that serum ferritin level remained as an independent predictive factor for poor PBSC mobilization. Our study indicated that transfusion-associated iron overload is a predictive factor for poor PBSC mobilization. Iron chelation therapy prior to apheresis may be required to collect sufficient numbers of PBSCs in the iron overload patients.