A proper balance between the n−3 and n−6 series of essential fatty acids (EFAs) is essential for homeostasis and normal growth in humans. Dietary supplement with fish oil and related n−3 EFAs has been used to study their antihypertensive property in animals and humans with borderline and essential hypertension. In the animal models, chronic treatment of young animals generally only attenuated the development of hypertension. In animals with hypercholesterolemia, n−3 EFA supplement increased the incidence of atherosclerosis. In humans, chronic treatment with fish oil only produced a small reduction in blood pressure. The concerns are that the high dose of fish oil may interfere with the control of blood glucose in diabetic patients, and may cause prolonged bleeding in surgical patients. Studies on the animal models of hypertension showed that n−6 EFAs are more effective than n−3 EFAs in lowering and normalizing the blood pressure of these animals, probably through the production of tissue prostaglandins, which favour vasodilation. The antihypertensive effect of the n−6 EFAs in humans is not well known, because mere are only a few studies, usually involving a very small number of patients. A possible side effect of n−6 EFAs for concern is that they might stimulate tumour development. A careful examination of these risk factors is needed before any recommendation can be made concerning the use of EFAs for the control of hypertension for humans.Key words: fish oil, essential fatty acid, hypertension, γ-linolenic acid.