Tissue electrolytes in the early phase of hypertension initiated by DCA have been compared with those in later persistent hypertension. In smooth muscle (aorta and stomach muscle) significant potassium depletion occurs during early hypertension in comparison with tissues from treated normotensive animals. A tendency for increased sodium concentration also developed. However, no significant changes from normotensive controls could be demonstrated in aorta during post-DCA, renal or spontaneous hypertension of long duration. These results suggest that there are differences in the disturbances in vascular smooth muscle electrolytes accompanying early and late hypertension. Differences in age or composition of the control groups and in the degree of hypertension produced may explain differences between these results and those of previous workers. None of the other tissues analyzed (left ventricle and psoas muscle) showed changes in electrolyte distribution characteristic of chronic hypertension.