Oxidative stress conditions such as oxidant stimuli, inflammation, exposure to xenobiotics and ionizing irradiation provoke cellular responses, principally involving transcriptional activation of genes encoding proteins that participate in the defense against oxidative tissue injuries. Excess of free heme, which is released from hemeproteins under these conditions, may constitute a major threat because it catalyzes the formation of reactive oxygen species. Exposure of mammalian cells to oxidative stimuli induces heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme degradation, as well as the 32-kDa heat shock protein. In various tissue injury systems, HO-1 induction has been shown to confer protection, while its abrogation has been shown to accelerate cellular injuries. In this review, recent findings concerning the role of HO-1 as a protective response against oxidative stress conditions are summarized, with a particular emphasis on its protective role in ischemic acute renal failure.