The effects of sodium DL-lactate and sodium chloride (2.5 mg/kg as 865 mmol/l solutions given by intravenous infusion over 20 min) on the renal tubular reabsorption of phosphate have been compared in five normal adults. 2. Sodium lactate produced a marked but transient increase in urinary phosphate excretion due to a reduction in net renal tubular reabsorption of phosphate; the mean value of the maximum rate of renal tubular reabsorption of phosphate/unit of glomerular filtration rate (TmP/GFR) decreased from 1.14 to 0.82 mmol/l. 3. This effect was not due simply to expansion of the volume of the extracellular fluid, since the reduction in TmP/GFR after sodium chloride infusion was less marked, nor did it seem to be due entirely to alkalinization of the urine since the maximum increase in urinary pH occurred 20--40 min after the maximum decrease in TmP/GFR.
