The washout of radioisotopes was studied in aorta, femoral artery and portal mesenteric vein from controls and rats made hypertensive with injection of deoxycorticosterone (DOC) acetate. Experiments were also conducted on tonic (pulmonary artery) and phasic (portal mesenteric vein) smooth muscle from rabbits. The rate constants for the washout of <sup>42</sup>K, <sup>36</sup>Cl and <sup>24</sup>Na from aorta were significantly elevated in the DOC hypertensives. Acute removal of extracellular K slowed the washout of <sup>24</sup>Na by 50%, however, the rate constant for the DOC group remained higher than the controls. Increased turnover of <sup>42</sup>K was also observed in the femoral artery and in a vessel (portal mesenteric vein) not exposed to the effects of high blood pressure in the rat. The rate constants for the washout of <sup>42</sup>K, <sup>36</sup>Cl and <sup>24</sup>Na from phasic smooth muscle in rabbit were greater than the tonic type. Ouabain significantly slowed <sup>24</sup>Na washout, however, the rate constant for the portal mesenteric vein remained higher than the pulmonary artery. DOC hypertension was associated with increased ion transport at several vascular sites. A similar change was observed for the phasic vascular smooth muscle from normal rabbits. A question is raised whether increased spontaneous activity of arteries reported to accompany DOC hypertension is the consequence of a membrane in transition from tonic to phasic behavior.