Twenty patients with a previous myocardial infarction were recruited into a randomised, double-blind, placebo-controlled, crossover trial of omega-3 fatty acid supplementation (2g/day for 6-weeks). Peripheral blood was taken for analysis of platelet and monocyte activation, and forearm blood flow was assessed in a subset of 12 patients during intrabrachial infusions of acetylcholine, substance P and sodium nitroprusside. Stimulated plasma tissue plasminogen activator (t-PA) concentrations were measured during substance P infusion.