Nitric oxide has high affinity for iron, and thus it can cause intracellular iron loss. We tested the idea that intracellular iron can be the primary target of NO toxicity by comparing the signaling mechanisms involved in cell death caused by iron depletion and that caused by NO. Treatment of HL‐60 cells with a NO donor, S‐nitroso‐ o‐N‐acetyl‐DL‐penicillamine (SNAP), decreased the intracellular iron level rapidly as that observed with the iron chelator deferoxamine (DFO). Iron chelators such as DFO and mimosine could induce death of human leukemic HL‐60 cells by a mechanism requiring activation of p38 kinase, c‐Jun N‐terminal kinase, caspase‐3 and caspase‐8. DFO and SNAP also caused release of cytochrome c from mitochondria. Inhibition of p38 kinase by a selective inhibitor, SB203580, abolished the NO and DFO‐induced cell death, release of cytochrome c, and activation of caspase‐3 and caspase‐8, thus indicating that p38 kinase lies upstream in the cell death processes. In a parallel situation, the cells t...