To demonstrate the influence of n-3 PUFA supplementation on cytokine and eicosanoid production in peripheral blood mononuclear cells (PBMCs) of MS patients (MSP), we investigated the impact of a 6-month dietary supplementation with these fatty acids on the levels of interleukin-1 beta (IL-1 beta), IL-2, interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in the supernatants of stimulated PBMCs and serum soluble IL-2 receptors in a group of 20 relapsing-remitting (R-R) MSP and a group of 15 age-matched control individuals (CI). The production of PGE2 and LTB4 in the stimulated PBMCs was also assessed in patient and control groups supplemented with n-3 PUFAs. In both groups, n-3 PUFA supplementation led to a significant decrease in the levels of IL-1 beta and TNF-alpha, and this reduction was more pronounced in the 3rd and 6th month of supplementation. An analogous decrease was observed in the levels of IL-2 and IFN-gamma produced by stimulated PBMCs, and in the levels of serum soluble IL-2 receptors. n-3 PUFA supplementation also appeared to significantly affect prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) production in PBMCs, both in MSP and the control group. The reduced production of these proinflammatory eicosanoids, and the decrease of some cytokines with an immunohenancing effect as a consequence of n-3 PUFA supplementation, could modulate some immune functions which have been demonstrated to be altered in MSP.