We recently reported that human inflammatory bowel disease mucosa contains large amounts of leukotriene B4, a potent chemotactic agent formed from arachidonic acid through the lipoxygenase pathway. To more fully evaluate the role of arachidonic acid metabolites in the mediation of intestinal inflammation, we studied arachidonate metabolism in an animal model: acetic acid colitis in the rat. Incubation of acetic acid colitis mucosa with arachidonic acid resulted in the production of leukotriene B4 and a series of monohydroxy fatty acids, all products of the lipoxygenase pathway, plus much smaller amounts of cyclooxygenase products including prostaglandin E2. All of these metabolities were made in significantly greater quantities by mucosa from acetic acid-treated rats than by controls. The pattern of arachidonate metabolism in acetic acid colitis was strikingly similar to that in human inflammatory bowel disease. Moreover, the concentration of leukotriene B4 in acetic acid-treated mucosa was almost identical to that in human inflammatory bowel disease mucosa and was 50 times greater than that in normal rat colonic mucosa. These data indicate that lipoxygenase products, including leukotriene B4, may be important mediators of intestinal inflammation in a wide variety of inflammatory conditions. Moreover, the similarities in the metabolism of arachidonate by human inflammatory bowel disease and by acetic acid colitis may allow the use of this model, and perhaps other animal models of intestinal inflammation, in the screening of potential therapeutic agents for inflammatory bowel disease.