Clinical and histological studies were made on magnesium-deficiency dermatitis produced on a new strain of hairless rats. Superoxide anion generation in polymorphonuclear leukocytes (PMNs) and the inhibitory effect of some antioxidants and anti-inflammatory agents against the elicited dermatitis were also examined. From the detection of increased superoxide production and effective actions of inhibitors including superoxide dismutase, cepharanthine, 4-4'-diamono-diphenylsulphone and 5,4,11,14-eicosatetraynoic acid (ETYA), it is indicated that superoxide anion or related activated oxygen may be responsible for magnesium-deficiency dermatitis as an inflammatory mediator and that the dermatitis may be related to lipoxygenase metabolites derived from arachidonic acid.