The present study was undertaken to investigate the effects of parenteral lipid emulsions (LE) enriched with n-3 fatty acids (n-3 FA) in experimental acute colitis. Seventy-four adult male Wistar rats were randomized into six groups, five of which had acetic acid-induced colitis. The animals received a fat-free diet and water ad libitum in individual metabolic cages. By a central venous catheter, saline was infused (0.5 ml/h) into the control groups CS (without colitis) and CC (with colitis), while the test groups received specific LE for 7 days. The n-3/n-6 FA ratio and the lipidic compositions regarding long chain (LCT) and medium chain (MCT) triglycerides were: group L--1:7.7 (LCT, n = 12), M--1:7.0 (MCT and LCT, n = 12), LW-3--1:4.5 (LCT plus n-3 FA, n = 12) and MW-3--1:3.0 (MCT and LCT plus n-3 FA, n = 13). The frequency of diarrhea, oral intake/body weight ratio, intestinal alterations, macrophage cellularity were evaluated and colonic concentrations of leukotrienes (LTB4, LTC4), prostaglandins (PGE2) and thromboxanes (TXB2) were measured. Groups M, MW-3 and LW-3 had less diarrhea than the CC group (P<0.05). Average oral intake/body weight ratio in MW-3 animals was comparable to the CS and better than the CC group. n-3 FA treated rats (LW-3 and MW-3) presented less intestinal inflammatory alterations than CC rats. Mucosal ulcer formation in MW-3 group did not differ from CS rats. M and MW-3 rats had less macrophages in the colon than the CC group. Compared with CC group, lower concentrations of LTB4 in the CS, LW-3 and MW-3 groups; of PGE2 in the CS, M and MW-3 groups; and of TXB2 in the CS and MW-3 groups were found. Mean concentrations of LTC4 did not differ among the groups. Thus, a LCT-containing LE with a low n-3-n-6 ratio does not modify inflammatory colitis manifestations; LE with a high n-3-n-6 ratio reduces diarrhea, preserves oral intake-weight ratio, attenuates morphological consequences and decreases colonic concentrations of inflammatory mediators; MCT/LCT-containing LE with 1:3 n-3-n-6 ratio exerts the most profound beneficial impact on the inflammatory response.