Ferritin is a multimeric protein that stores 30% of human body iron as oxidised crystalline ferric phosphate, mainly in liver and heart muscle and in haemopoetic tissue and endothelium. Ascorbate causes iron release from ferritin by reducing stored iron (Km≈ 2 mM). Raised concentrations of non-protein bound iron catalyse formation extracellular and intracellular reactive oxygen species (1). Since intracellular and extracellular concentrations of ascorbate are generally within the range 40-250µM, this process is considered unlikely to contribute to pathological oxidation reactions. Only when ascorbate is raised > 2mM by i.v. injection is it deemed to be pro-oxidant (2). However, we have observed that ascorbate-dependent ferrous iron loss from horse spleen ferritin 50 nM (Sigma-Aldrich, UK), monitored for 2-3 h using a plate reader at 24°C to detect changes in absorption of ferrozine at 562µm (pH 7.0 buffered with sodium citrate 10 mM; MOPS 50 mM and 75µM ferrozine) is synergized by ferrous iron > 2 µM). Raising Fe(II) from 0 to 10µM decreases the Km of ascorbate-dependent Fe(II) release to 185±10µM (P < 0.001) and increases the Vmax of release 5-fold from 11.4±0.2 to 60±2.0 nmol Fe(II) mg-1ferritin min-1(P < 0.001). In the absence of external iron, hydrogen peroxide acts as a potent non-competitive inhibitor of Vmax of ascorbate-dependent iron release by promoting two electron Fe(II) oxidation within ferritin( I.C50 111±34 µM). The IC50 of H2O2 on the apparent Km of ascorbate-dependent Fe(II) release is 352±92µM; addition of 10 µM Fe(II) with superoxide dismutase (50 units ml-1) reduces the IC50 to H2O2 30±42µM (P < 0.01) without altering the Vmax of Fe(II) release. Thus, H2O2 changes from a non-competitive inhibitor of ascorbate dependent of Fe(II) release in the absence of external Fe(II) to a competitive inhibitor when Fe(II) is present. These results suggest that single electron reactions generated by iron-ascorbate interaction, possibly resulting from ascorbyl and ferryl radical are a potent means of iron reduction and release from ferritin (3,4) and that this release mode differs from that caused by ascorbate alone, which may reduce bound di-Fe(III) at the ferroxidase centre by a bidentate two-electron reduction. Our novel finding that ascorbate and iron synergistically exacerbate iron release from ferritin has many implications relating to inflammatory mechanisms, the most immediate provides a rationale for iron-chelation therapy of arthritis and atherosclerosis, where iron and ascorbate and H2O2 released from necrotic macrophages and endothelium provide essential substrates for Fenton-Haber-Weiss reactions continuously generating superoxide and ●OH radicals (5).