In an attempt to standardize conditions for quantitating proteinuria, we examined the effect of water loading and intravenous administration of furosemide on protein excretion in man. Urine volume, protein excretion, and creatinine clearance increased in both studies, and there was significant correlation between percentage changes in protein excretion and creatinine clearance. We recommend that protein excretion rate should be determined during short periods under standard conditions of posture, hydration, and ideally, without interference by drugs.