Laboratory animal models and clinical studies suggest that dietary n-3 fatty acids are beneficial in diseases with an inflammatory component such as rheumatoid arthritis or psoriasis. In the present study we investigated the effect of purified docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on phorbol ester (TPA)-induced acute inflammation. Mice were fed for 6 weeks a diet containing 5% corn oil enriched with either 1% DHA or 1% EPA and compared with a group receiving 6% corn oil only. The dietary treatment with DHA or EPA elevated the n-3 polyunsaturated fatty acids as expected in the spleen and ear phospholipids, associated with a reduction in arachidonic acid levels. The degree of ear inflammation was quantified by measuring the four parameters including (1) edema as the increase in ear biopsy weight, (2) polymorphonuclear cell infiltration as myeloperoxidase activity (MPO) at the site of inflammation, (3) prostaglandin E2 (PGE2) and (4) leukotriene B4 (LTB4) concentrations in ear edema. The addition of DHA to the diet reduced significantly the edema formation and the MPO activity 24 h after TPA challenge. Both DHA and EPA significantly reduced the PGE2 and LTB4 levels compared with animals fed corn oil. This result suggests that DHA rather than EPA may be useful in the adjuvant treatment of diseases where acute inflammatory processes play a role.