Eicosanoids and platelet-activating factor (PAF) production increases in experimental colitis. Both eicosanoids and PAF seem to arise from similar membrane phospholipids. To support both these suggestions we have investigated whether a fat-free diet, which should alter production of eicosanoids and PAF, affects experimental colitis. Essential fatty acid deficient (EFAD) rats were obtained by putting 4-week-old animals on a fat-free diet for 3 months. Experimental colitis was induced by a single intracolonic administration of 2 ml of 4% acetic acid. One to seven days later the animals were sacrificed and the colon removed to assess macroscopically and histologically intestinal damage. Eicosanoids and PAF levels were also measured in the mucosa scrapings by specific radioimmunoassay. The injury to the colon was more evident in control rats compared with EFAD rats. Besides colonic tissue of control rats showed a highly significant increase of PGE2, LTB4 and PAF, compared with levels in EFAD rats. Our results indicate that fat-free diet reduces tissue damage, and at the same time PGE2, LTB4 and PAF colonic content.