The effect of aldosterone (1 microgram/kg X h) on the urinary excretion of lithium (Li) was measured by clearance studies in adrenalectomized rats receiving a glucocorticoid substitution (dexamethasone 6.6 micrograms/kg). Aldosterone induced significant anti-natriuresis and kaliuresis. The fractional excretion of Li remained constant around 28% and was not modified by aldosterone during the experiment (4 h). These results indicate that the tubular reabsorption of Li is not directly dependent on mineralocorticoid hormones. The previously reported effects of long term administration of DOCA or spironolactone of Li excretion are probably secondary to modifications of the sodium balance which, in turn, influences the proximal Li reabsorption rate.