Hypertension is linked to disturbed total-body sodium (Na(+)) regulation; however, measuring Na(+) disposition in the body is difficult. We implemented (23)Na magnetic resonance spectroscopy ((23)Na-MR) and imaging technique ((23)Na-MRI) at 9.4T for animals and 3T for humans to quantify Na(+) content in skeletal muscle and skin. We compared (23)Na-MRI data with actual tissue Na(+) content measured by chemical analysis in animal and human tissue. We then quantified tissue Na(+) content in normal humans and in patients with primary aldosteronism. We found a 29% increase in muscle Na(+) content in patients with aldosteronism compared with normal women and men. This tissue Na(+) was mobilized after successful treatment without accompanying weight loss. We suggest that, after further refinements, this tool could facilitate understanding the relationships between Na(+) accumulation and hypertension. Furthermore, with additional technical advances, a future clinical use may be possible.