Summary.Non‐transferrin‐bound iron (NTBI) in plasma is toxic due to its ability to participate in free radical formation with resultant peroxidation and damage to cell membranes and other biomolecules. NTBI concentration was determined in serum in 12 normal volunteers and in 52 patients with β‐thalassaemia major by a modification of the method described by Singhet al(1990). There was no detectable NTBI in normal individuals. In the patients NTBI values ranged from −1.5 to 9.0 μmol/l (mean ± SD: 3.6 ± 2.3). The patients’serum ferritin concentrations ranged from 207 to 11400 μg/l (2674±2538), total serum iron from 20 to 61 μmol/l (39.5 ± 9.6) and transferrin saturation from 44 to 110 (84.5 ± 13.8). The NTBI correlated significantly with serum ferritin (r=0.467,P<0.001), total serum iron (r=0.608,P<0.001) and transferrin saturation (r=0.481,P<0.005). When patients were grouped according to their compliance with desferrioxamine (DFX) therapy, the good compliers had significantly lower NTBI concentrations compared to the poor compliers (poor: 5.4±1.8 μmol/lvgood: 2.7±1.7 μmol/l,P<0.001). There was also a significant difference between the level of NTBI and whether or not the patients had complications of iron overload (5.2±1.7 μmol/lv2.9±1.6 μmol/l,P<0.001). During this study 10 patients were entered into a trial of the oral iron chelator 1,2‐dimethy 1–3‐hydroxypyrid‐4‐one (L1). Their NTBI values were observed during the first 6 months of the trial and showed a significant fall (paired t‐test:P= 0.007). These results suggest that the level of NTBI may prove helpful in assessing the efficiency of chelation in patients with transfusion dependent an
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