We evaluated the phosphate-binding efficiency of Sorbiphos, a non-toxic aluminium-free natural polymer, in five volunteers aged 28-34 years with normal renal function. After an overnight fast, a placebo, 2 g of Sorbiphos or a therapeutic dose of Alu-Cap (950 mg) were given, 30 min before a dietary load of phosphorus. Serum and urinary phosphate were measured on hourly samples. A similar increment in serum and urine phosphate was noted after the ingestion of placebo or Sorbiphos, but both serum and urine phosphate increased less after Alu-Cap. Since the recommended dose of Sorbiphos is half that of Alu-Cap, we conclude that Sorbiphos has little phosphate-binding efficiency in normal subjects given moderate phosphate loads.