The aim of the present study was to assess the effect of calcium infusion on segmental tubular reabsorption in humans using lithium clearance, along with creatinine and free water clearances during maximal water diuresis. In 8 healthy volunteers, a 20-min 5 mg/kg calcium infusion that increased serum calcium levels from 2.27 ± 0.07 to 2.87 ± 0.07 mmol/l (p