The present study was conducted to determine whether half the dose of elemental calcium given as acetate (Ca Ac) could control on medium term the predialysis plasma phosphate as well as calcium carbonate (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, Ca Ac, in 12 compliant patients on chronic dialysis previously treated by Ca CO3. Because of poor tolerance of Ca Ac during the first period 4 patients were excluded and the results have been assessed only on the 8 patients who completed the study. For half the doses of elemental calcium (620 +/- 250 mg versus 1310 +/- 560 mg versus 710 +/- 200 mg/day) Ca acetate allowed the same control of predialytic hyperphosphatemia (1.67 +/- .34; 1.74 +/- .32; 1.75 +/- .38) with paradoxically comparable normal mean plasma calcium concentration (2.61 +/- .14; 2.56 +/- .13; 2.55 +/- .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. We conclude that calcium acetate controls predialytic hyperphosphatemia as efficiently as CaCO3 for half the dose of elemental calcium without however decreasing the frequency of hypercalcemia.