Tioxamast is an antiallergic drug that inhibits anaphylaxis in various models in rats, and it inhibits the release and synthesis of certain mediators of inflammation [see Tarayre et al., this issue]. Here we report that the drug also has an anti-inflammatory effect in vivo in various nonimmunological models in rats. It reduces zymosan-induced inflammation in the paw and pleural cavity, starting at doses from 1.5625 to 3.125 mg/kg given intraperitoneally. In pleurisy, tioxamast lowers the concentration of leukotriene B4 (LTB4) in the exudate, at doses from 50 mg/kg i.p. Also, at doses from 12.5 mg/kg i.p., the compound reduced PAF-acether-induced pleurisy and the concentrations of LTB4 and peptidoleukotrienes in the exudate. An anti-inflammatory action against carrageenin-induced edema of the paw was seen only at doses of 50 mg/kg i.p. or more. The anti-inflammatory and antiallergic effect of tioxamast makes it a potentially useful drug in the treatment of allergies in humans.