Thirty healthy male volunteers were randomly allocated into two dietary treatment groups. The flaxseed group (n = 15) maintained a diet high in alpha-linolenic acid (alpha-LA; 18:3n-3) and low in linoleic acid (LA; 18:2n-6) by using a flaxseed oil and spread that are high in alpha-LA. The control group (n = 15) maintained a diet high in LA and low in alpha-LA, typifying a Western diet. Both groups maintained their diets for 4 wk, followed by another 4-wk period in which they supplemented the diets with fish oil [1.62 g eicosapentaenoic acid (EPA, 20:5n-3) daily and 1.08 g docosahexaenoic acid (DHA, 22:6n-3) daily] in a triglyceride form. The flaxseed oil-containing diet resulted in significant increases in alpha-LA concentrations in the plasma phospholipid, cholesteryl ester, and triglyceride fractions (eightfold increase) and neutrophil phospholipids (50% increase). EPA concentrations increased by 2.5-fold in the plasma lipid fractions and neutrophil phospholipids. After fish-oil supplementation EPA concentrations increased in parallel in both dietary groups, remaining higher in the flaxseed group for both the plasma lipid fractions and neutrophil phospholipids. The results indicate that alpha-LA-rich vegetable oils can be used in a domestic setting (in conjunction with a background diet low in LA) to elevate EPA in tissues to concentrations comparable with those associated with fish-oil supplementation.