The consumption of EPA and DHA has been associated with reduced risk for cardiovascular disease morbidity and mortality. Mean intakes of EPA and DHA in the United States and elsewhere are below levels recommended by health authorities. The main non-marine source of dietary (n-3) fatty acids (a-linolenic acid) is poorly converted to EPA in humans. Stearidonic acid (SDA) is a non-marine fatty acid that appears to be more readily converted to EPA in humans. Results from previous studies suggested that SDA, relative to EPA, increases RBC EPA, with reported efficiencies ranging from ˜16 to 30%. A recently published, randomized, single-blind, controlled, parallel group study in healthy men and women characterized the relationships between intakes of SDA and EPA and EPA enrichment of RBC membranes over a 12-wk period. %EPA in RBC membranes was greater after EPA (0.44, 1.3, or 2.7 g/d, respectively) and SDA (1.3, 2.6, or 5.2 g/d, respectively) consumption compared to a safflower control (all P < 0.02). Based on quadratic response surface models, for EPA intakes of 0.25, 0.50, and 0.89 g/d, SDA intakes of 0.61, 1.89, and 5.32 g/d, respectively, would berequired to produce equivalent values for RBC % EPA, translating to relative efficiencies of 41.0, 26.5, and 16.7%. Thus, dietary SDA over a range of intakes increases RBC % EPA, with declining relative efficiency as SDA intake increases. J. Nutr. 142: 626S-629S, 2012.