Vascular responsiveness to nitroprusside and to norepinephrine was examined in two different preparations from DOCA hypertensive and normotensire control Spraguehyphendawley rats. The bloodhyphenperfused renal vascuiatures of DOCA hypertensive rats were significantly more sensitive than those of normotensiTe controls to the vasodilator action of low doses of nitroprusside. At high doses, responses in DOCA hypertensive and normotensive rats were similar. Since basal “structural” vascular resistances were greater in the hypertensive rats, it is possible that further vasodilation with nitroprusside was impeded more in DOCAtreated than in control rats. Nitroprusside produced a greater degree of vascular smooth muscle relaxation in tail artery strips from DOCA hypertensive rats than in those from normotensive controls. The current study is the first characterization of the effects of a vasodilator in mlneralocortlcoM hypertension. The two preparations gave divergent results with respect to vascular sensitivity to norepinephrine. When compared with control rats, the DOCA hypertensive rats showed a greater sensitivity to norepinephrine in tail arteries but a lesser renal vascular reactivity. It is evident that one must take a number of variables into consideration when characterizing changes in vascular responses that occur in a given model of hypertension: 1) the region of the vasculature (renal vs caudal artery); 2) the level of the arterial tree (conduit vs resistance vessels); 3) the technique employed for measurement of vascular changes (smooth muscle contraction vs vascular resistance changes); 4) the initial vasoconstrictor tone of the preparation; and 5) the agonist used (nitroprusside vs norepinephrine). (Hypertension 4: 13–19, 1982)