1. α-Human atrial natriuretic peptide (7.5 pmol min−1 kg−1) was infused intravenously into eight healthy men after pretreatment with lithium carbonate (750 mg) or placebo.
2. Baseline sodium excretion was significantly increased after lithium, but the natriuresis during infusion of α-human atrial natriuretic peptide was attenuated.
3. Similar decreases in plasma renin activity with infusion of α-human atrial natriuretic peptide occurred on both days.
4. Administration of lithium may be associated with pharmacological effects and further work is required to validate the use of lithium clearance as a marker of proximal renal tubular sodium handling.