The cytokines interleukin-1 and tumor necrosis factor-alpha are potent peptide mediators of the immune response. They exert potent cellular effects at nanomolar concentrations with target tissues ranging from the vascular endothelium, to the central nervous system and immunocompetent cells. The synthesis of these two cytokines can be suppressed pharmacologically by steroids and other immunosuppressive agents such as cyclosporin A. In previous studies we have found that such an inhibition of inflammatory cytokine synthesis can also be achieved by increasing the content of n-3 polyunsaturated fatty acids in leukocyte membranes.