Non-transferrin-bound iron (NTBI) emerges in plasma of patients with systemic iron overload, but has also been documented in further pathological conditions. Quantification of NTBI can be useful for diagnosis and management of these disorders. However, currently available detection methods are tedious and often inaccurate, hampering wide applicability. In this issue of the Biochemical Journal, Ma et al. report the development of a novel assay for NTBI measurement, based on an iron-sensitive fluorescent probe that is linked to magnetic beads. The approach offers several advantages over existing technology and may bring NTBI assessment closer to the clinic.