Summary: The aim of this study was to compare the alimentary phosphate‐binding capacity of calcium acetate to calcium carbonate in stable chronic renal failure patients who were not on haemodialysis. Intestinal absorption of phosphate and calcium was measured on three occasions in five patients with chronic renal failure who were not on maintenance haemodialysis. During each test period they received either no drug, calcium carbonate or calcium acetate (both containing 1g elemental calcium) in a randomized manner, along with a standardized meal. Intestinal contents were recovered after 10h by whole gut lavage, and phosphorus and calcium measured in meal and intestinal contents. Faecal excretion of ingested phosphorus increased from 13.85% in the absence of drug to 29.91% after calcium carbonate administration. Phosphorus excretion was significantly higher after calcium acetate (43.92%) compared to calcium carbonate ( P <0.05). Less calcium was absorbed from calcium acetate than from equimolar amounts of calcium caronate ( P <0.05). In patients with stable renal failure, calcium acetate is a better alimentary phosphate binder than calcium carbonate and binds more phosphorus for each mol of calcium absorbed.