We investigated the effects of BW 755C, an inhibitor of both the cyclooxygenase and lipoxygenase pathways of arachidonic acid metabolism; FPL 55712, a selective antagonist of slow-reacting substance of anaphylaxis; and indomethacin, a cyclooxygenase inhibitor, on bronchial reactivity after ozone exposure. Guinea pigs in groups of 5 were treated with BW 755C (10 mg/kg given intravenously), FPL 55712 (5 mg/kg given intravenously), or indomethacin (30 mg/kg given intraperitoneally) and studied before and 30 min after a 15-min exposure to 3.0 ppm ozone. These animals were compared with a similarly exposed group that was untreated (n = 10). Reactivity was determined by measuring specific airway resistance (SRaw) upon intravenous acetylcholine infusion in unanesthetized, spontaneously breathing animals. Prior to ozone exposure, we found that drug treatment did not affect either SRaw or muscarinic reactivity. After exposure to 3.0 ppm, all untreated guinea pigs showed substantial muscarinic hyperreactivity. Indomethacin treatment did not inhibit this effect. Furthermore, in the indomethacin-treated animals, marked elevations in SRaw after ozone occurred. In contrast, no change in SRaw or muscarinic reactivity occurred after ozone in any animal treated with either BW 755C or FPL 55712. We conclude that ozone-induced bronchial hyperreactivity in the guinea pig rapidly develops after a brief, high-level exposure. This effect may be mediated in part by lipoxygenase products derived from lung arachidonic acid metabolism post-ozone period.