A case of acute phosphorus poisoning with hypocalcemia and hypophosphatemia with recovery is presented. The urinary calcium and phosphate excretion data–obtained when significant hypocalcemia and hypophosphatemia were present and considered in relation to the estimated oral intake and creatinine clearance–provided evidence for hypercalciuria and hyperphosphaturia. Other renal abnormalities included very slight aminoaciduria, pyuria, hematuria and proteinuria, transient azotemia, and occasional glycosuria when FBS ranged from 100–117 mg/100 ml in a patient with probable diabetes mellitus. The studies of urinary concentrating and acidifying mechanisms were consistent with preservation of these functions. These observations suggest that disturbance of proximal tubular function particularly may occur in acute phosphorus poisoning.