Since Mai et al. found, with the intestinal lavage technique, that the same dose of elemental calcium given as acetate (Ca Ac) complexed in the gut of uremic patients twice as much phosphate as calcium carbonate (CaCO3) while inducing a rather low calcium absorption, we wanted to see if half the dose of elemental calcium given as Ca Ac could control, on medium term, the predialysis plasma phosphate as well as CaCO3 while inducing less frequent hypercalcemia. This was evaluated in a cross-over study of 3 periods of 10 weeks according to the sequence Ca Ac, CaCO3 and Ca Ac, in 12 compliant patients on chronic dialysis previously treated by CaCO3. Because of poor tolerance of Ca Ac during the first period, 4 patients were excluded and the results were assessed only on the 8 patients who completed the study. For half the doses of elemental calcium (620 ± 250 mg versus 1,310 ± 560 mg versus 710 ± 200 mg/day), Ca Ac allowed the same control of predialytic hyperphosphatemia (1.67 ± 0.34; 1.74 ± 0.32; 1.75 ± 0.38) with paradoxically comparable normal mean plasma calcium concentration (2.61 ± 0.14; 2.56 ± 0.13; 2.55 ± 0.14 mmol/l). Plasma alkaline phosphatases and intact PTH concentrations remained also stable during the 3 periods. The frequency of hypercalcemia greater than 2.75 mmol/l (12; 9; 20%) and of hyperphosphatemia greater than 2 mmol/l (17; 22; 27%) were comparable with the 2 treatments. In conclusion, Ca Ac controls predialytic hyperphosphatemia as efficiently as CaCO3 for half the dose of elemental calcium without, however, decreasing the frequency of hypercalcemia. These results challenge the validity of extrapolating the results of the intestinal lavage technique for assessing the medium-term absoφtion of calcium. The real advantage of Ca Ac over CaCO3 as phosphate binder remains to be es