We tested the hypothesis that substitution of omega-3 fat for dietary omega-6 fat would reduce mortality and decrease Kupffer cell prostaglandin E2 (PGE2) production in a rat model of chronic sepsis. Rats were fed via gastrostomy for 12 days with isonitrogenous, isocaloric diets containing 15% of calories as either safflower oil (omega-6) or a 10:1 mixture of menhaden oil (omega-3) and safflower oil. After five days of feeding, animals received an intra-abdominal abscess of defined bacterial content. Survivors were killed on post-laparotomy day 6 in conjunction with liver perfusion and protease liver digestion for Kupffer cell isolation. Kupffer cell PGE2 production was measured by radioimmunoassay after 18 hours of cell culture and again after stimulation with 0 LPS, 10 ng/ml LPS, and 10 micrograms/LPS. Mortality was decreased in menhaden oil-fed animals compared with safflower oil-fed animals (16% vs. 35%). Kupffer cell PGE2 production was decreased in menhaden oil-fed animals at 18 hours (354 +/- 54 vs. 570 +/- 95 pg/0.1 ml; p = 0.09) and after stimulation with 10 micrograms/ml LPS (140 +/- 41 vs. 288 +/- 45 pg/0.1 ml; p = 0.03) compared with safflower oil-fed animals.