Adult male unanesthetized rats, reared on a diet enriched in both α-linolenic acid (α-LNA) and docosahexaenoic acid (DHA), were infused intravenously for 5 min with [1-14C]α-LNA. Timed arterial samples were collected until the animals were killed at 5 min and the brain was removed after microwaving. Plasma and brain lipid concentrations and radioactivities were measured. Within plasma lipids, > 99% of radioactivity was in the form of unchanged [1-14C]α-LNA. Eighty-six per cent of brain radioactivity at 5 min was present as β-oxidation products, whereas the remainder was mainly in ‘stable’ phospholipid or triglyceride as α-LNA or DHA. Equations derived from kinetic modeling demonstrated that unesterified unlabeled α-LNA rapidly enters brain from plasma, but that its incorporation into brain phospholipid and triglyceride, as in the form of synthesized DHA, is ≤ 0.2% of the amount that enters the brain. Thus, in rats fed a diet containing large amounts of both α-LNA and DHA, the α-LNA that enters brain from plasma largely undergoes β-oxidation, and is not an appreciable source of DHA within brain phospholipids.