The quantity of leukotrienes produced in an inflammation model, the stimulated mouse peritoneum, was affected by dietary manipulation of tissue arachidonic acid, the immediate leukotriene (LT) precursor. Fifty ng of LTE4 was synthesized (after injection of zymosan) by the peritoneal cavity of mice maintained on olive oil as a dietary source of unsaturated fatty acids. Animals maintained on corn oil, exhibited significantly enhanced leukotriene biosynthesis upon stimulation by zymosan. Mice fed menhaden oil, a fat source rich in n-3 fatty acids produced 50% less leukotriene E4 than animals fed olive oil. The results indicated that production of leukotrienes, potent mediators of inflammatory reactions, are affected by the type of polyunsaturated fatty acids in the diet.