1. Renal lithium clearance in healthy men was elevated while the subject was reclining, decreased upon standing and increased upon lying down during 45–60 min tests.
2. Parallel changes in renal clearance of creatinine, sodium and potassium, and urine flow rate occurred in response to the changes in posture.
3. The findings demonstrate for the first time that posture is a factor that can influence lithium excretion. Control of posture during lithium excretion tests is recommended.