Excessive or inadequate inflammation contributes to the range of acute and chronic human diseases and is characterized by the production of inflammatory cytokines, eicosanoids derived from arachidonic acid, reactive oxygen forms and adhesive molecules. The main substrate for eicosanoid synthesis (i.e. prostaglandins, thromboxanes, leukotrienes and other oxidated derivates), is n-6 (ω-6) PUFA arachidonic acid. n-3 (ω-3) PUFA [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] lower origination of inflammatory mediators and expression of adhesive molecules. They replace the arachidonic acid as a substrate for eicosanoids and block its metabolism. In IBD patients several randomized placebo controlled double blind studies were performed with fish oil, which showed improvement of the clinical score, lower percentage of relapses and decrease in use of corticosteroids.