This article is available online at http://www.jlr.org An impact on arterial stiffness and compliance, associated with reduced blood pressure (1–4), is thought to be a significant contributor to the lower CVD risk associated with increased long chain n-3 PUFA (LC n-3 PUFA; EPA plus DHA) intake and status (4–6). In randomized controlled trials (RCTs) conducted to date, vascular function is typically measured in the fasting nonchallenged state. Given that adults following Westernized dietary patterns typically spend 16–18 h per day in the postprandial state, and that a postprandial phenotype characterized by an exaggerated lipemia and glycemia and inflammatory and oxidative stress is associated with vascular dysfunction (7), the postprandial vascular response is likely to be a more significant and discriminating marker of CVD risk. However, the impact of dietary factors and meal composition on acute postprandial vascular function is poorly understood. Increasing the total fat content of a test meal reduces both cardiac and peripheral postprandial vascular reactivity (7) and a small number of studies providing EPA plus DHA in the test meal have reported a positive effect of fish oil on vascular tone over 2–8 h (8–12). Although rarely considered, variability in the EPA and DHA ratio of the n-3 PUFA (fish or fish oil) source used in RCTs is likely to be a major determinant of the apparent inconsistency in findings reported. Abstract Our objective was to investigate the impact of EPA versus DHA on arterial stiffness and reactivity and underlying mechanisms (with a focus on plasma oxylipins) in the postprandial state. In a three-arm crossover acute test meal trial, men (n = 26, 35–55 years) at increased CVD risk received a high-fat (42.4 g) test meal providing 4.16 g of EPA or DHA or control oil in random order. At 0 h and 4 h, blood samples were collected to quantify plasma fatty acids, long chain n-3 PUFA-derived oxylipins, nitrite and hydrogen sulfide, and serum lipids and glucose. Vascular function was assessed using blood pressure, reactive hyperemia index, pulse wave velocity, and augmentation index (AIx). The DHA-rich oil significantly reduced AIx by 13% (P = 0.047) with the decrease following EPA-rich oil intervention not reaching statistical significance. Both interventions increased EPAand DHAderived oxylipins in the acute postprandial state, with an (1.3fold) increase in 19,20-dihydroxydocosapentaenoic acid evident after DHA intervention (P < 0.001). In conclusion, a single dose of DHA significantly improved postprandial arterial stiffness as assessed by AIx, which if sustained would be associated with a significant decrease in CVD risk. The observed increases in oxylipins provide a mechanistic insight into the AIx effect.—McManus, S., N. Tejera, K. Awwad, D. Vauzour, N. Rigby, I. Fleming, A. Cassidy, and A. M. Minihane. Differential effects of EPA versus DHA on postprandial vascular function and the plasma oxylipin profile in men. J. Lipid Res. 2016. 57: 1720–1727.