This experiment was designed to study the effects in fattening steers of n-6 PUFA supplementation on the plasma distribution and chemical composition of major lipoproteins (TG-rich lipoproteins: d< 1.006 g/mL; intermediate density lipoproteins + LDL 1.019 < d < 1.060 g/mL; light HDL 1.060 < d < 1.091 g/mL; and heavy HDL: 1.091 < d < 1.180 g/mL). For a period of 70 d, animals [454 +/- 20 d; 528 +/- 36 kg (mean +/- SD)] were given a control diet (diet C, n = 6) consisting of hay and concentrate mixture (54 and 46% of diet dry matter, respectively) or the same diet supplemented with sunflower oil (4% of dry matter), given either as crushed seeds (diet S, n = 6) or as free oil continuously infused into the duodenum through a chronic canula to avoid ruminal PUFA hydrogenation (diet 0, n = 6). Plasma lipids increased in steers given diet S (x 1.4, P < 0.05) and diet O (x2.3, P < 0.05), leading to hyperphospholipemia and hypercholesterolemia. With diet S, hypercholesterolemia was associated with higher levels of light(x1.4, P < 0.05) and heavy H DL (x1.3, NS). With diet O, it was linked to higher levels of light HDL (x1.8. P < 0.005) and to very light HDL accumulation within density limits of 1.019 to 1.060 g/mL, as demonstrated by the apolipoprotein Ad profile. Diet O favored incorporation of 1 8:2n-6 into polar (x2.2, P < 0.05) and neutral lipids (x1.5 to x8, P < 0.05) at the expense of SFA, MUFA, and n-3 PUFA. Thus, protection of dietary PUFA against ruminal hydrogenation allowed them to accumulate in plasma lipoproteins, but the effects of hypercholesterolemia on animal health linked to very light HDL accumulation remain to be elucidated.