Heme oxygenase-1 (HO-1) is a stress-responsive enzyme that catabolizes free heme into carbon monoxide, iron (which induces the expression of heavy-chain ferritin, an iron-sequestering protein) and biliverdin (which is converted to bilirubin by biliverdin reductase). Over the past few years it has become apparent that these ‘arms' of the HO-1 system can act protectively in a variety of experimental models of disease; there is also evidence that HO-1 and bilirubin have protective actions in humans. Here, we present a model for the beneficial actions of the products of heme degradation, and we discuss the potential clinical applications of enhancing the HO-1 system.