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Traditionally hand-pressed argan oil, obtained from Argania spinosa seeds, is eaten raw in south-west Morocco; its rich composition of tocopherols, MUFA and PUFA make a study of its actions on risk factors for CVD, such as hypertension, interesting. The effects of 7 weeks of treatment with argan oil (10 ml/kg) on the blood pressure and endothelial function of spontaneously hypertensive rats (SHR) and normotensive Wistar -Kyoto rats were investigated. Systolic blood pressure and heart rate were measured every week by the tailcuff method and endothelial function was assessed by carbachol (10 28 to 10 24 M)-induced relaxations of aortic rings and small mesenteric arteries pre-contracted with phenylephrine. Argan-oil administration reduced the mean blood pressure of SHR after the fifth week of treatment (P, 0·05) and increased (P, 0·01) the endothelial responses of arteries from SHR. The NO synthase inhibitor, L-N-v-nitroarginine (3 £ 10 25 M) revealed a greater participation of NO in the relaxant effect after the treatment. When cyclooxygenase (COX) was blocked with indomethacin (10 25 M), an involvement of COX products in the endothelium-dependent response was characterized. Enzyme immunoassay of thromboxane B 2 showed a significant decrease (P, 0·05) in the release of thromboxane A 2 in both aorta and small mesenteric artery after argan-oil treatment of SHR. Experiments in the presence of the thromboxane A 2 -prostaglandin H 2 receptor antagonist ICI 192,605 (10 25 M) confirmed this result. Results after incubation with the antioxidants superoxide dismutase and catalase suggested that a decreased oxidative stress might contribute to explain the beneficial effects of argan-oil treatment.