Despite the apparent consensus on the existence of endothelial dysfunction in conduit and resistance arteries of spontaneously hypertensive rats (SHR), a commonly employed experimental model of hypertension, there are a number of reports showing that endothelium-dependent vasodilatory responses are similar, or even increased, in SHR compared with their normotensive counterparts. The present paper aims to discuss the rationale for these apparent discrepancies, including the effect of age, type of artery and methodological aspects. Data from the literature indicate that the age of the animal is a contributing factor and that endothelial dysfunction is likely to be a consequence of hypertension. In addition, the use of antioxidant additives, such as ascorbic acid or ethylene diaminetetraacetic acid, and differences in the level of initial arterial stretch, might also be of importance because they may modify the oxidative status of the artery and the levels of vasoactive factors released by the endothelium.