Heme oxygenase (HO)-1 may have an important role in the resolution of T cell-mediated inflammation. The authors elucidated the role of the anti-inflammatory HO-1 in the pathogenesis of skin inflammation, using a mouse contact hypersensitivity (CHS) induced by 2,4-dinitrofluorobenzene (DNFB). Ear swelling was induced by challenge with DNFB, accompanied by infiltration of inflammatory cells in the challenged ear skin. DNFB challenge induced low levels of HO-1 mRNA and protein expression. Ear swelling induced by DNFB challenge was significantly reduced by topical treatment with cobalt protoporphyrin IX (CoPP), a HO-1 inducer, but exaggerated by blockage of HO-1 activity with tin protoporphyrin IX (SnPP), a HO-1 inhibitor. Similarly, the number of infiltrated cells in DNFB-challenged ear skin were reduced by CoPP but increased by SnPP. Our findings suggest that HO-1 plays an important role in CHS and is an important pharmacological target for the treatment of CHS.