1. 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.