Cerebral blood flow (CBF) was measured in 40 regions of the rat central nervous system by the [14C]iodoantipyrine autoradiographic technique during a moderate elevation in mean arterial blood pressure (to ca. 150 mmHg), induced by i.v. infusion of either dopamine (DA) or noradrenaline (NA). Hypertension induced by DA resulted in significant increases (median = 44%) in local CBF in 38 of the 40 brain regions investigated. In contrast, during NA infusion, CBF was elevated only slightly (median = 15%) in a few (8 of 40) brain regions (P less than 0.05). The cerebrovascular response to hypertension appears to be dependent upon the catecholamine which is employed to elicit the elevation in arterial blood pressure.