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e Summary. For large scale exposures of the human population to ionising radiation, there is a need for cost-effective high throughput assessment of radiation exposure levels from biological samples to allow triage decisions to be made. Here we discuss the usefulness of the DNA damage marker γ-H2AX for this purpose. Foci of γ-H2AX form in response to radiation-induced DNA double-strand breaks and can be quantified by immunofluorescence microscopy or flow cytometry. Several studies have analysed this marker in patients ’ blood samples to determine radiation exposures dur-ing various diagnostic or therapeutic radiation treatments. Such planned exposures involve only a moderate number of samples which can be obtained at a prearranged time following exposure. In contrast, application of this method as a triage tool in large scale radiological emergencies demands high throughput sample processing and analysis. The rapid kinetics of γ-H2AX induction and loss presents a major challenge to its successful application as a triage tool. These and other as yet unre-solved questions are discussed. Key words: γ-H2AX, double-stranded DNA break, triage, biological dosimetry, radiation accident. Riassunto (γ-H2AX come biomarcatore dell’esposizione a radiazioni). In presenza di un’esposizione