We evaluated the effect of one session of biofiltration on calcium-phosphate metabolism in four uremic patients and compared the results with those of a previous traditional hemodialysis (Cuprophane membrane) session, on the same subjects. The most noteworthy results were: both total and ionized plasma calcium rose less in biofiltration; phosphate clearance and parathyroid hormone clearance were higher in biofiltration; plasma 25-OH D did not change in either dialysis technique.