Flaxseed oil is the most abundant plant source of omega-3 fatty acid, alpha-linolenic acid omega-3. This review focuses on the biological effects of dietary alpha-linolenic acid (ALA) compared with long-chain omega-3 derivatives. ALA is not equivalent in its biological effects to the long-chain omega-3 fatty acids found in marine fish oils. However, ALA is metabolized to eicosapentaenoic acid, which may replace arachidonic acid in membrane phospholipides. Ingestion of flaxseed oil may alter the generation of eicosanoids, procoagulant activity and other membrane-dependent responses and exert antiallergic, antiatherosclerotic, antiarrhythmic effects. Beneficial effects of flaxseed oil have been shown in prevention and management of cardiovascular disease.