Sulfur mustard (2,2`-dichlorodiethyl sulfide), a radiomimetic agent with mutagenic (Cappizzi et al., 1973; Fox and Scott, 1983), cytotoxic (Wheeler, 1962; Papirmeister and Davison, 1965), and vesicant (Anslow and Houck, 1946; Renshaw, 1946) properties, is also a chemical-warfare blistering agent with no known antidote. Sulfur mustard predominantly effects exposed epithelial tissues of the skin, the eye, and the respiratory tract, although higher doses can produce systemic toxicity (reviewed by Papirmeister et al., 1991). The severity of sulfur mustard toxicity is dose dependent, causing irritation, edema, necrosis and ulceration; characteristic symptoms are unique to the site of exposure, e.g., vesication, conjunctivitis, bronchopneumonia (reviewed by Papirmeister et al., 1991). The basic histopathology of mustard-induced cutaneous lesions has been reviewed by Papirmeister et al. (1985, 1991) and includes degeneration of epidermal cells, especially in the basal layer, followed by the formation of vesicles (and, in man, bullae) that have been variously characterized as intraepidermal or subcorneal but that appear in most cases to result from cleavage at the dermal-epidermal junction. However, despite general agreement concerning the morphologic changes caused by mustard and despite more than 50 years of research, the pathogenesis of mustard injury is still incompletely understood.