Twenty hypertensive subjects participated in three clinical trials of 13 days each, to examine the effects of Alsepa fish oil [20:5, n-3 eicosapentaenoic acid (EPA) 180 mg, and 22:6 n-3 docosahexaenoic acid (DHA) 120 mg] on n-3 for n-6 polyunsaturated fatty acids (PUFA) exchange on serum phospholipids, blood pressure (BP), triglycerides (TG) and primary hemostasis. After 13 days, plasma phospholipids showed an increase in sigma n-3 (EPA and DHA) from 2.0 to 5.9% (P < 0.01), and a decrease in sigma n-6 (arachidonic acid and linoleic acid) from 29.8 to 22.6% (P < 0.01). A concomitantly significant reduction in systolic BP (SBP) (158.7 +/- 23.8 mm Hg to 146.5 +/- 17.0 mm Hg, P = 0.04), and diastolic BP (DBP) (80.8 +/- 8.4 mm Hg to 72.9 +/- 14.9 mm Hg, P = 0.04) as well as a significant decrease in platelet adhesion and aggregation on extra cellular matrix measured as a percentage of surface coverage (11.9 +/- 4.8% to 4.2 +/- 3.2%, P = 0.0001) was observed. In addition, a significant reduction in baseline dependent TG was observed; the higher the baseline level TG, the more pronounced the reduction (average 159.2 +/- 74.6 mg% to 108.0 +/- 46.1 mg%, P = 0.001). No change was observed in total cholesterol, high and low density lipoprotein (HDL, LDL), platelet and fibrinogen. Repeated fasting and refeeding with fish oil facilitated plasma exchange of n-3 for n-6 PUFA, improved BP, clinical metabolic parameters and lowered platelet reactivity in the vessel wall (primary hemostasis). In severe and life-threatening situations, the beneficial effects of fish oil should be considered for rapid exchange of n-3 for n-6 PUFA. In this study we describe a novel approach for rapid fatty acid exchange by fasting/refeeding with fish oil supplementation, as well as improved BP, plasma lipids and primary hemostasis. Further research is required on the therapeutic use of fish oils and the physiological mechanisms involved in fatty acid exchange.