Iron has been shown to be important in ischaemic, immune and toxic forms of tissue injury in various organs. Although it is generally accepted that iron participates in the generation of powerful oxidant species (e.g. hydroxyl radicals) there has not been any direct evidence that iron capable of catalysing free-radical reactions is increased in tissues in these models of injury. In the present study we demonstrate that ischaemia/reperfusion injury to the kidney results in no significant change in total, nonhaem or ferritin iron levels, but there is a marked and specific increase in bleomycin-detectable iron (capable of catalysing free-radical reactions) in the kidney. The increase in bleomycin-detectable iron is observed only after reperfusion but not during the ischaemic period. In a separate study we demonstrate that despite a drastic reduction in the iron content in the kidney, as a result of feeding an iron-deficient diet, there is a similar and a marked increase in the bleomycin-detectable iron in kidneys accompanied by a lack of protection against ischaemia/reperfusion injury.