Sulfur mustard (SM), a potent vesicant and chemical warfare agent, induces tissue damage involving an inflammatory response, including vasodilatation, polymorphonuclear infiltration, production of inflammatory mediators, and cyclooxygenase activity. To evaluate the role of cyclooxygenase-1 and -2 (COX-1, COX-2) in sulfur mustard-induced skin toxicity, we applied the agent to the ears of wildtype (WT) and COX-1- and COX-2-deficient mice. In the latter, ear swelling 24 and 48 h after exposure was significantly reduced (P < 0.05) by 55% and 30%, respectively, compared to WT. Quantitative histopathology revealed no epidermal ulceration in COX-2-deficient mice but some degree of severity in WT. COX-2-deficient mice showed significant reductions (P < 0.05) in severity of epidermal necrosis (29%), acute inflammation (42%), and hemorrhage (25%), compared to the WT mice. COX-1 deficiency resulted in significant exacerbation (P < 0.05) in severity of some parameters, including increases of 4.6- and 1.2-fold in epidermal ulceration and epidermal necrosis, respectively, compared to WT. Postexposure treatment of normal male ICR mice with the selective COX-2 inhibitor celecoxib resulted in significant reductions of 27% (P < 0.05) and 28% (P < 0.01) in ear swelling at intervals of 40 and 60 min between exposure and treatment, respectively. Histopathological evaluation revealed significant reductions (P < 0.05) in subepidermal microblister formation (73%) and dermal necrosis (32%), compared to the control group. These findings may indicate that COX-2 participates in the early stages of sulfur mustard-induced acute skin toxicity and that COX-1 might exert some protective function against this chemical insult.