Intragastric ethanol stimulates mucosal formation of leukotriene C4 in the rat stomach. The present study demonstrates that the increase in leukotriene C4 formation begins within 30 seconds and is maximal within 5 minutes, closely paralleled by the appearance of hemorrhagic lesions. Leukotriene C4 formation returns to prechallenge levels within 3 hours, although erosions still persist. Intragastric 0.2N NaOH, acidified 100 mmol/L taurocholate, 25% NaCl, or 0.6N HCl did not consistently increase leukotriene C4 formation despite severe mucosal injury. A number of sulfhydryl-containing or sulfhydryl-blocking agents as well as metals protected against mucosal damage and simultaneously prevented the stimulation of leukotriene C4 formation induced by ethanol. None of the agents increased and some virtually abolished mucosal formation of prostaglandin E2, indicating that gastroprotection can occur completely independently of the endogenous prostaglandin system. The leukotriene biosynthesis inhibitor MK-886 markedly suppressed gastric leukotriene C4 formation but did not protect against damage caused by ethanol, NaOH, NaCl, or acidified taurocholate. Oral indomethacin reduced the ex vivo formation of both prostaglandin E2 and, to a lesser extent, leukotriene C4 in the gastric mucosa, inducing a shift in the balance from protective prostaglandins to proulcerogenic leukotriene C4. Pretreatment with MK-886, however, did not significantly diminish indomethacin-induced lesions. These data suggest that leukotriene C4 is not the exclusive mediator of gastric injury caused by necrotizing agents or indomethacin. On the other hand, certain protective compounds exhibit a striking parallelism between protection and inhibition of ethanol-induced leukotriene C4 formation, suggesting that they may affect a target crucial for both mucosal injury and stimulation of 5-lipoxygenase.